Fluororesin, fluororesin particles, and methods for producing these

ABSTRACT

The present invention relates to resin particles including a residue unit represented by the following general formula (1) and having a volume average particle diameter equal to or more than 5 μm and equal to or less than 2000 μm, and a method for producing thereof. Furthermore the present invention relates to a fluororesin comprising a residue unit represented by a general formula (1) and having a weight average molecular weight Mw in a range of 5×104 to 3×105, and a yellow index of a heat-melted molded product (thickness 3 mm) after 24 h at 280° C. of equal to or less than 6, and a method for producing thereof.In the formula (1), Rf1, Rf2, Rf3, and Rf4 are each independently one of the groups consisting of a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms. The perfluoroalkyl group may have an ethereal oxygen atom. Further, Rf1, Rf2, Rf3, and Rf4 may be linked to one another to form a ring having 4 or more and 8 or less carbon atoms, and the ring may include an ethereal oxygen atom.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. § 371 national stage patentapplication of International patent application PCT/JP2019/038144, filedon Sep. 27, 2019, which is based on and claims the benefits of priorityto Japanese Patent Application No. 2018-183594, filed on Sep. 28, 2018,Japanese Patent Application No. 2019-027318, filed on Feb. 19, 2019,Japanese Patent Application No. 2019-171553, filed on Sep. 20, 2019, andJapanese Patent Application No. 2019-037005, filed on Feb. 28, 2019. Theentire contents of all of the above applications are incorporated hereinby reference.

TECHNICAL FIELD

The first aspect of the present invention relates to fluororesinparticles having excellent flowability and filling property, and to amethod for producing the same. The second aspect of the presentinvention relates to a fluororesin and a method for producing the same.

BACKGROUND ART

Fluororesins have excellent heat resistance, electrical properties,chemical resistance, waterproofness, liquid-repellent and oil-repellentproperties, and optical properties, and hence are used for protectivefilms for electronic components such as semiconductors, water-repellentfilms for inkjet printer heads, and water protection oil coatings forfilters, and optical members.

Among them, a fluororesin including an oxolane ring has a bulky ringstructure, and therefore is amorphous and has high transparency and highheat resistance. In addition, since such a fluororesin is composed onlyof carbon, fluorine and oxygen, the fluororesin has high electricalproperties, chemical resistance, waterproofness and liquid-repellentoil-repellent properties. Furthermore, since the fluororesin isamorphous, it can be melt-molded.

PTL 1 describes a polymer ofperfluoro(2-methylene-4-methyl-1,3-dioxolane (PFMMD)) as a fluororesinincluding an oxolane ring, and a method for producing the same. Example2 of PTL 1 describes an example in which a polymer ofperfluoro(2-methylene-4-methyl-1,3-dioxolane) is polymerized in theco-presence of nitrogen fluoride (N₂F₂) in a glass sealed tube. In thisexample, no solvent is used, and there is no description of a specificform of the obtained polymer. NPL 1 describes performing bulkpolymerization or solution polymerization of PFMMD to obtain apoly-PFMMD, which is a polymer thereof, as a fluororesin including anoxolane ring. In the present description, a resin and a polymer aredescribed as synonymous with each other unless otherwise specified.

-   [Patent Literature (PTL) 1] U.S. Pat. No. 3,308,107-   [Non-Patent Literature (NPL) 1] Macromolecules 2005, 38, 4237

The entire descriptions of PTL 1 and NPL 1 are incorporated herein as ifspecifically disclosed herein.

SUMMARY OF INVENTION Technical Problem

NPL 1 indicates that in the case of bulk polymerization, wherepurification is not performed after the polymerization, opticalproperties and heat resistance of the described resin are deterioratedand that, however, this deterioration is reduced by purification. Insolution polymerization, after polymerization is carried out usingeither of two types of fluorine-including solvents, chloroform is addedfor precipitation. There is no description of a specific form of thebulk-polymerized resin after purification or the resin obtained byadding chloroform to cause precipitation.

As a result of the study by the present inventors, it was found that theresins obtained by the methods described in PTL 1 and NPL 1 had anindeterminate non-particulate form. Therefore, there was a problem inflowability of the resin. For example, it has been found that when theresin was melt-molded, there was a problem in handling such asdifficulty in continuously supplying the resin to the inside of amolding machine. Further, since the resins described in PTL 1 andNon-PTL 1 have the above-mentioned form, it was established that, forexample, when the resin is filled in the molding machine, the resin of adesired weight cannot be filled with respect to a predetermined volume,that is, there is a problem of a low filling property. In this respect,since a container, having a large volume for the weight of the resin, isrequired, there is also a problem that cost-efficiency is lowered whentransporting the article.

Therefore, an object of the first aspect of the present invention is toprovide resin particles including a residue unit represented by ageneral formula (1) that have excellent flowability and fillingproperty, and a method for producing the same, in order to solve theabove-mentioned problems.

In addition, the results of further studies by the present inventorshave shown that the resin produced by the methods described in PTL 1 andNPL has an indeterminate non-particulate form, and therefore, it isdifficult to remove the solvent incorporated inside the resin. In a casewhere the solvent remains in the resin, the amount of weight loss inheating is large, and there is also a problem that foaming or the likeoccurs during molding, or the working environment during molding isdeteriorated.

Therefore, an object of the first aspect of the present invention is toprovide resin particles including a residue unit represented by ageneral formula (1) that have not only excellent flowability and fillingproperty, but also a small amount of weight loss in heating, and amethod for producing the same.

In addition, in the production of a fluororesin, it is generallypossible to obtain resin particles by means such as emulsionpolymerization and suspension polymerization. However, in these methods,an emulsifier or a dispersant is used as a polymerization aid. However,the emulsifier or dispersant used may become a foreign substance byremaining inside the resin particles, and may further cause coloringwhen the resin is heated, which may impair transparency and heatresistance. It may be possible that the strict cleanliness required, inrecent years, for semiconductor peripheral members could not besatisfied.

Therefore, an object of the first aspect of the present invention is toprovide a method for producing resin particles including a residue unitrepresented by the general formula (1) which are excellent inflowability and filling property, without using an emulsifier and/or adispersant, and also to provide resin particles including a residue unitrepresented by the general formula (1), which do not contain anemulsifier and/or a dispersant.

Further, an object of the first aspect of the present invention is toprovide resin particles including a residue unit represented by generalformula (1) which are not only excellent in flowability and fillingproperty, but also have a small amount of weight loss in heating and donot contain an emulsifier and/or a dispersant, and also to provide amethod for producing the resin particles.

Although poly-PFMMD is excellent in heat resistance, according to thestudy by the present inventors, it has a high melt viscosity, inferiormelt molding processability, and also inferior defoaming property at thetime of heating and melting, and shows significant yellowing afterheating and melting.

Lowering the molecular weight of a polymer is effective in lowering themelt viscosity and improving the melt molding processability. Accordingto NPL 1, the molecular weight can be reduced by using carbontetrabromide (CBr₄) as a chain transfer agent. However, as a result ofstudies by the present inventors, it has been established that thepolymer reduced in molecular weight by using carbon tetrabromide (CBr₄)as a chain transfer agent described in NPL 1 has a problem thatyellowing after heating and melting is significant.

An object of the second aspect of the present invention is to solve theproblems inherent to the fluororesins including the above mentionedoxolane ring, and specifically, to provide a fluororesin including anoxolane ring which is excellent in melt molding processability and inwhich yellowing after heating and melting is suppressed.

Furthermore, reducing the molecular weight of a polymer also lowers theglass transition temperature. Heat resistance is impaired by loweringthe glass transition temperature. In addition, as a result of studies bythe present inventors, it has been established that where carbontetrabromide (CBr₄) is used as a chain transfer agent to reduce themolecular weight, there is a problem that cracks occur during coolingafter heat molding. Further, in NPL 1, nothing is mentioned about meltviscosity, defoaming property at the time of melting, and crackgeneration, and the characteristics of the resin that achieves bothdefoaming property at the time of melting and resistance to crackgeneration are not clarified, and moreover the characteristics of theresin that satisfies all of the defoaming property at the time ofmelting, resistance to crack generation, heat resistance, and meltviscosity are not clarified. NPL 1 also describes a polymerizationexample using a chain transfer agent other than carbon tetrabromide(CBr₄), but as a result of the studies by the present inventors, it hasbeen found that such polymerization does not produce a resin excellentin melt molding processability in which yellowing after heating andmelting is suppressed. Further, there is no resin that has bothdefoaming property and resistance to crack generation, and there is noresin that combines all of defoaming property at the time of melting,resistance to crack generation, heat resistance, and melt viscosity.

Further, as a result of studies by the present inventors, it has beenestablished that the polymer reduced in molecular weight by the methodusing carbon tetrabromide (CBr₄) as the chain transfer agent describedin NPL 1 had the problems that the amount of weight loss changessignificantly during holding at 300° C. for a certain period of time andthat thermal decomposition is likely to occur.

An object of the second aspect of the present invention is also toprovide a fluororesin which includes an oxolane ring, and which excelsin melt molding processability, and in which yellowing after heating andmelting is suppressed, and moreover which has low melt viscosity,excellent heat resistance and defoaming property at the time of melting,and shows less cracking during cooling after heat molding.

Solution to Problem

The present inventors have found that novel resin particles including aresidue unit represented by a following general formula (1) and having avolume average particle diameter of 5 μm or more and 2000 μm or lesshave excellent flowability and filling property, and this has led to thecompletion of the first aspect of the present invention.

In the formula (1), Rf₁, Rf₂, Rf₃, and Rf₄ are each independently one ofthe groups consisting of a fluorine atom, a linear perfluoroalkyl grouphaving 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to7 carbon atoms, and a cyclic perfluoroalkyl group having 3 to 7 carbonatoms. The perfluoroalkyl group may have an ethereal oxygen atom.Further, Rf₁, Rf₂, Rf₃, and Rf₄ may be linked to one another to form aring having 4 or more and 8 or less carbon atoms, and the ring mayinclude an ethereal oxygen atom.

Furthermore, the present inventors have found that by using aprecipitation polymerization method, resin particles can be obtainedwithout using an emulsifier or a dispersant, that the resin particlesobtained without using an emulsifier or a dispersant do not contain anemulsifier or a dispersant and retain the original transparency and heatresistance of the resin, and that resin particles, inside which nosolvent remains and which have a small amount of weight loss in heating,can be obtained, and thus have arrived at a preferred embodiment of thefirst aspect of the present invention.

The first aspect of the present invention is as follows.

[1-1]

The resin particles including a residue unit represented by thefollowing general formula (1) and having a volume average particlediameter equal to or more than 5 μm and equal to or less than 2000 μm.

(In the formula (1), Rf₁, Rf₂, Rf₃, and Rf₄ are each independently oneof the groups consisting of a fluorine atom, a linear perfluoroalkylgroup having 1 to 7 carbon atoms, a branched perfluoroalkyl group having3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7carbon atoms. The perfluoroalkyl group may have an ethereal oxygen atom.Further, Rf₁, Rf₂, Rf₃, and Rf₄ may be linked to one another to form aring having 4 or more and 8 or less carbon atoms, and the ring mayinclude an ethereal oxygen atom).[1-2]

The resin particles according to [1-1], wherein the volume averageparticle diameter is equal to or more than 5 μm and equal to or lessthan 500 μm.

[1-3]

The resin particles according to [1-1] or [1-2], wherein an angle ofrepose is equal to or more than 5° and equal to or less than 60°.

[1-4]

The resin particles according to any one of [1-1] to [1-3], wherein theresin particles are a precipitation polymerization polymer.

[1-5]

The resin particles according to any one of [1-1] to [1-4], wherein abulk density is equal to or more than 0.2 g/mL and equal to or less than1.5 g/mL.

[1-6]

The resin particles according to any one of [1-1] to [1-5], wherein theamount of weight loss in heating at 250° C. is equal to or less than 1%by weight.

[1-7]

The resin particles according to any one of [1-1] to [1-6], wherein theresin particles do not contain an emulsifier and/or a dispersant.

[1-8]

The resin particles according to any one of [1-1] to [1-7], wherein theresidue unit represented by the general formula (1) is aperfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit representedby a general formula (2).

[1-9]

A method for producing the resin particles according to any one of [1-1]to [1-7], the method comprising:

-   -   a step of obtaining a resin including a residue unit represented        by a general formula (4) by placing a mixture of a radical        polymerization initiator, a monomer represented by a following        general formula (3) and an organic solvent under polymerization        conditions, wherein    -   the organic solvent is a solvent in which at least the monomer        is dissolved, at least a part of the resin produced by the        polymerization is not dissolved, and precipitation of the resin        occurs; and    -   the resin produced by the polymerization precipitates as        particles in the organic solvent.

(In the formula (3), Rf₅, Rf₆, Rf₇, and Rf₈ are each independently oneof the groups consisting of a fluorine atom, a linear perfluoroalkylgroup having 1 to 7 carbon atoms, a branched perfluoroalkyl group having3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7carbon atoms. The perfluoroalkyl group may have an ethereal oxygen atom.Further, Rf₅, Rf₆, Rf₇, and Rf₈ may be linked to one another to form aring having 4 or more and 8 or less carbon atoms, and the ring mayinclude an ethereal oxygen atom).

(Definitions of Rf₅, Rf₆, Rf₇, and Rf₈ in the formula (4) are the sameas definitions of Rf₅, Rf₆, Rf₇, and Rf₈ in the formula (3),respectively.)[1-10]

The production method according to [1-9], wherein the organic solvent isan organic solvent dissolving the monomer represented by the generalformula (3) and does not dissolve the resin including a residue unitrepresented by the general formula (4).

[1-11]

The production method according to [1-10], wherein the organic solventis an organic solvent in which after resin particles including a residueunit represented by the general formula (4) and having a weight averagemolecular weight Mw of 5×10⁴ to 70×10⁴ have been immersed at 50° C. for5 h or more in the organic solvent in an amount 10 times (w/w) that ofthe organic particles, a residue of the resin particles is visuallyconfirmed in the organic solvent.

[1-12]

The production method according to [1-10] or [1-11], wherein the organicsolvent is an organic solvent in which resin particles including aresidue unit represented by the general formula (4) and having a weightaverage molecular weight Mw of 5×10⁴ to 70×10⁴ are immersed at 50° C.for 5 h or more in the organic solvent in an amount 10 times (w/w) thatof the organic particles, the solvent is thereafter cooled to 25° C., aresin sample remaining in a solid state is recovered, and a weight lossratio of the resin sample is less than 20% by weight.

[1-13]

The production method according to any one of [1-9] to [1-12], whereinan organic solvent comprising a fluorine atom and a hydrogen atom in amolecule is used.

[1-14]

The production method according to [1-13], wherein the organic solventhaving a hydrogen atom amount equal to or more than 1% by weight in thesolvent molecule is used.

[1-15]

The manufacturing method according to any one of [1-9] to [1-14],wherein the monomer represented by the general formula (3) isperfluoro(4-methyl-2-methylene-1,3-dioxolane) represented by a generalformula (5), and the residue unit represented by the general formula (4)is a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unitrepresented by a general formula (6).

The second aspect of the present invention is as follows.

[2-1]

A fluororesin comprising a residue unit represented by a general formula(1) and having a weight average molecular weight Mw in a range of 5×10⁴to 3×10⁵, and a yellow index of a heat-melted molded product (thickness3 mm) after 24 h at 280° C. of equal to or less than 6.

In the formula (1), Rf₁, Rf₂, Rf₃, and Rf₄ are each independently one ofthe group consisting of a fluorine atom, a linear perfluoroalkyl grouphaving 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbonatoms, the perfluoroalkyl group may have an ethereal oxygen atom, Rf₁,Rf₂, Rf₃, and Rf₄ may be linked to one another to form a ring having 4or more and 8 or less carbon atoms, and the ring may include an etherealoxygen atom.[2-2]

The fluororesin according to [2-1], wherein a glass transitiontemperature is equal to or higher than 125° C. and equal to or lowerthan 145° C.

[2-3]

The fluororesin according to [2-1] or [2-2], wherein a melt viscosity ata shear rate of 10⁻² s and 250° C. is 1×10² to 3×10⁵ Pa·s.

[2-4]

The fluororesin according to any one of [2-1] to [2-3], which has amolecular weight distribution Mw/Mn of 1.2 to 8.

[2-5]

The fluororesin according to any one of [2-1] to [2-4], wherein thenumber of cracks in the heat-melted molded product (thickness 3 mm,diameter 26.4 mm) after 24 h at 280° C. is equal to or less than 10.

[2-6]

The fluororesin according to any one of [2-1] to [2-5], wherein adifference B−A between an amount A of weight loss immediately after thetemperature is raised to 300° C. at 10° C./min in air in TG-DTA and anamount B of weight loss after the temperature is raised to 300° C. andthen held at 300° C. for 30 min is equal to or less than 1.0%.

[2-7]

The fluororesin according to any one of [2-1] to [2-6], wherein an areaoccupied by bubbles in the heat-melted molded product (thickness 3 mm,diameter 26.4 mm) after 24 h at 280° C. is equal to or less than 10%relative to an area of the molded product.

[2-8]

The fluororesin according to any one of [2-1] to [2-7], wherein thenumber of bubbles in the heat-melted molded product (thickness 3 mm,diameter 26.4 mm) after 24 h at 280° C. is 10 or less.

[2-9]

The fluororesin according to any one of [2-1] to [2-8], wherein theweight average molecular weight Mw is in a range of 5×10⁴ to 2×10⁵.

[2-10]

The fluororesin according to any one of [2-1] to [2-9], wherein a meltviscosity at a shear rate of 10⁻² s and 250° C. is 1×10² to 5×10⁴ Pa·s.

[2-11]

The fluororesin according to any one of [2-1] to [2-10], including aresidue unit represented by a following general formula (2).

[2-12]

A method for producing a fluororesin, the method comprising obtaining afluororesin that includes a residue unit represented by a followinggeneral formula (4) by polymerizing a monomer represented by a followinggeneral formula (3) in the presence of a radical polymerizationinitiator and a chain transfer agent, wherein the chain transfer agentis an organic compound having 1 to 20 carbon atoms and including atleast one atom selected from the group consisting of a hydrogen atom anda chlorine atom, and the fluororesin has a weight average molecularweight Mw in a range of 5×10⁴ to 3×10⁵ and has a yellow index of aheat-melted molded product (thickness 3 mm) after 24 h at 280° C. ofequal to or less than 6.

(In the formula (3), Rf₅, Rf₆, Rf₇, and Rf₈ are each independently oneof the group consisting of a fluorine atom, a linear perfluoroalkylgroup having 1 to 7 carbon atoms, a branched perfluoroalkyl group having3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7carbon atoms, the perfluoroalkyl group may have an ethereal oxygen atom,Rf₅, Rf₆, Rf₇, and Rf₈ may be linked to one another to form a ringhaving 4 or more and 8 or less carbon atoms, and the ring may include anethereal oxygen atom).[2-13]

The production method according to [2-12], wherein an amount of thechain transfer agent is 3% by weight to 50% by weight based on a totalamount of the monomer and the chain transfer agent.

[2-14]

The production method according to [2-12] or [2-13], wherein thepolymerization is carried out in an organic solvent that dissolves themonomer represented by the general formula (3) and precipitates thefluororesin including a residue unit represented by the general formula(4).

[2-15]

The production method according to any one of [2-12] to [2-14], whereinthe chain transfer agent is an organic compound having 1 to 20 carbonatoms and including a chlorine atom.

[2-16]

The production method according to any one of [2-12] to [2-15], whereinthe chain transfer agent is an organic compound having 1 to 20 carbonatoms and including a chlorine atom and a hydrogen atom.

Advantageous Effects of Invention

According to the first aspect of the present invention, it is possibleto provide fluororesin particles having excellent flowability andfilling property and a method for producing the fluororesin particles.

Further, according to the first aspect of the present invention, it ispossible to provide resin particles which are not only excellent inflowability and filling property but also do not contain an emulsifieror a dispersant, and a method for producing the same, and also provideresin particles which are not only excellent in flowability and fillingproperty but also have a small amount of weight loss in heating, and amethod for producing the same.

According to the second aspect of the present invention, it is possibleto provide a fluororesin including an oxolane ring, which is excellentin heat resistance and melt molding processability and in whichyellowing after heating and melting is suppressed. Further, according tothe second aspect of the present invention, it is possible to provide afluororesin including an oxolane ring, which excels in heat resistanceand melt molding processability, in which yellowing after heating andmelting is suppressed, and which also has low melt viscosity, excellentdefoaming property at the time of melting, and shows less crackingduring cooling after heat molding.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1-1 shows a particle diameter distribution of resin particlesproduced in Example 1-1.

FIG. 1-2 shows a particle diameter distribution of resin particlesproduced in Example 1-4.

FIG. 2-1 is a photograph of the fluororesin of Example 2-1 after heatingat 280° C. for 24 h, melting and cooling.

FIG. 2-2 is a photograph of the fluororesin of Example 2-4 after heatingat 280° C. for 24 h, melting and cooling.

FIG. 2-3 is a photograph of the fluororesin of Example 2-5 after heatingat 280° C. for 24 h, melting and cooling.

FIG. 2-4 is a photograph of the fluororesin of Comparative Example 2-1after heating at 280° C. for 24 h, melting and cooling.

FIG. 2-5 is a photograph of the fluororesin of Comparative Example 2-2after heating at 280° C. for 24 h, melting and cooling.

FIG. 2-6 is a photograph of the fluororesin of Comparative Example 2-3after heating at 280° C. for 24 h, melting and cooling.

DESCRIPTION OF EMBODIMENTS

The first aspect of the present invention will be described in detailbelow.

The first aspect of the present invention is resin particles including aresidue unit represented by the general formula (1). Since thefluororesin particles of the present invention have a bulky ringstructure included in the general formula (1), the fluororesin particlesare amorphous and have high transparency and high heat resistance.Moreover, since the fluororesin particles are composed only of carbon,fluorine and oxygen, the fluororesin particles have high electricalproperties, chemical resistance, waterproofness and liquid-repellentoil-repellent property.

The Rf₁, Rf₂, Rf₃, and Rf₄ groups in the residual unit represented bythe general formula (1) in the first aspect of the present invention areeach independently one of the group consisting of a fluorine atom, alinear perfluoroalkyl group having 1 to 7 carbon atoms, a branchedperfluoroalkyl group having 3 to 7 carbon atoms, or a cyclicperfluoroalkyl group having 3 to 7 carbon atoms. The perfluoroalkylgroup may have an ethereal oxygen atom. Further, Rf₁, Rf₂, Rf₃, and Rf₄may be linked to one another to form a ring having 4 or more and 8 orless carbon atoms, and the ring may include an ethereal oxygen atom.

Examples of the linear perfluoroalkyl group having 1 to 7 carbon atomsinclude a trifluoromethyl group, a pentafluoroethyl group, aheptafluoropropyl group, a nonafluorobutyl group, an undecafluoropentylgroup, a tridecafluorohexyl group, and a pentadecafluoroheptyl group;examples of the branched perfluoroalkyl group having 3 to 7 carbon atomsinclude a heptafluoroisopropyl group, a nonafluoroisobutyl group, anonafluorosec-butyl group, and a nonafluorotert-butyl group; andexamples of the cyclic perfluoroalkyl group having 3 to 7 carbon atomsinclude a heptafluorocyclopropyl group, a nonafluorocyclobutyl group,and a tridecafluorocyclohexyl group. Examples of the linearperfluoroalkyl group which has 1 to 7 carbon atoms and may have anethereal oxygen atom include a —CF₂OCF₃ group, a-(CF₂)₂OCF₃ group, and a—(CF₂)₂OCF₂CF₃ group; examples of the cyclic perfluoroalkyl group whichhas 3 to 7 carbon atoms and may have an ethereal oxygen atom include a2-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, a4-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, and a2-(2,3,3,4,4,5,5-heptafluoro)-furanyl group.

In order to obtain excellent heat resistance, it is preferable that atleast one of Rf₁, Rf₂, Rf₃ and Rf₄ be one of the group consisting of alinear perfluoroalkyl group having 1 to 7 carbon atoms, a branchedperfluoroalkyl group having 3 to 7 carbon atoms, and a cyclicperfluoroalkyl group having 3 to 7 carbon atoms.

Examples of the residue unit represented by the general formula (1)include the following residue units.

Among these, resin particles including the following residue units arepreferable because they are excellent in heat resistance and moldingprocessability, and a resin includingperfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit representedby the formula (2) is more preferable.

As a result of having the volume average particle diameter of 5 μm ormore and 2000 μm or less, the resin particles of the present inventionhave high flowability and can be continuously supplied to a moldingmachine or the like. The volume average particle diameter is preferably5 μm or more and 1000 μm or less. Further, since the volume averageparticle diameter is in the above range, the solvent can be preventedfrom remaining in the resin particles, so that the amount of weight lossin heating is small. The solvent can also remain in the resin particleswhen the resin particles are obtained by the precipitationpolymerization method described hereinbelow.

It is more preferable that the resin particles of the present inventionhave a volume average particle diameter of 5 μm or more and 500 μm orless. As a result of the volume average particle diameter being in thisrange, a higher flowability is obtained, continuous supply to a moldingmachine or the like is facilitated, and the amount of weight loss inheating is also reduced. Further, the filling property is increased ascompared with the resin obtained by the method described in NPL 1, andthe resin can be efficiently stored in a container. Where the volumeaverage particle diameter is 5 μm or more, the particles are unlikely tobe scattered by an air flow, and the handleability of the resinparticles of the present invention is improved. Further, it ispreferable that the volume average particle diameter be 500 μm or lessbecause the resin particles can be melted in a shorter time and theefficiency of the molding process is improved.

The 90% particle diameter of the resin particles of the presentinvention is preferably 2500 μm or less, more preferably 2000 μm orless, and further preferably 1000 μm or less. As a result, in the resinparticles of the present invention, the amount of coarse particles islowered, and the flowability and moldability are further improved.

Further, the resin particles of the present invention preferably have a10% particle diameter of 3 μm or more. As a result, in the resinparticles of the present invention, the amount of fine particles islowered, dusting is further prevented, and flowability is furtherimproved.

The volume average particle diameter, 90% particle diameter, 10%particle diameter, and particle diameter distribution of the resinparticles of the present invention can be evaluated by particle diameterdistribution measurement (volume distribution) by a laser diffractionscattering method. The particle diameter distribution by the laserdiffraction/scattering method is measured after the resin particles aredispersed in water or an organic solvent such as methanol and, ifnecessary, treated with an ultrasonic homogenizer to homogenize thedispersed state of the particles, whereby quantification can beperformed with good reproducibility. As a laser scattering meter,MICROTRACK manufactured by Microtrack Bell Co., Ltd. can be exemplified.

The volume average particle diameter is also called a Mean VolumeDiameter, which is an average particle diameter expressed on a volumebasis. The particle diameter distribution is divided for each particlediameter channel, and assuming that the representative particle diametervalue of each particle diameter channel is d, and the volume-basedpercentage for each particle diameter channel is ν, the volume averageparticle diameter is represented by Σ(νd)/Σ(ν).

The 10% particle diameter represents the particle diameter at a pointwhere the cumulative amount is 10% when the cumulative amount iscalculated with the total volume of the powder group as 100%. The 90%particle diameter represents the particle diameter at a point where thecumulative amount is 90% when the cumulative amount is calculated withthe total volume of the powder group as 100%.

The resin particles of the present invention preferably do not includean emulsifier and/or a dispersant. As a result of not including anemulsifier and/or a dispersant, the resin and resin particles havingexcellent transparency and heat resistance can be obtained. Resinparticles including no emulsifier and/or dispersant can be produced byusing a precipitation polymerization method described hereinbelow.Therefore, the resin particles of the present invention are preferably aprecipitated polymer. Here, the dispersant is an agent having a functionof dispersing resin particles in a solvent, and examples thereof includepolyvinyl alcohol, methyl cellulose, hydroxypropyl methyl cellulose,hydroxyethyl methyl cellulose, and the like. The emulsifier is an agenthaving a function of emulsifying resin particles in a solvent, andexamples thereof include fluorine-including surfactants such as sodiumperfluorooctanate, sodium perfluorooctane sulfonate, ammoniumperfluorooctanate, and the like; fluorine-free surfactants such assodium lauryl sulfate, ethylene glycol-based polymers, and the like; andthe like.

The bulk density of the resin particles of the present invention ispreferably 0.2 g/cm³ or more and 1.5 g/cm³ or less from the viewpoint ofobtaining filling property. The bulk density can be measured by themethod described in Examples described hereinbelow.

The resin particles of the present invention may include other monomerresidue units, and examples of the other monomer residue units includetetrafluoroethylene (TFE), hexafluoropropylene (HFP), andchlorotrifluoroethylene (CTFE), trifluoroethylene,hexafluoroisobutylene, perfluoroalkylethylene, fluorovinyl ether, vinylfluoride (VF), vinylidene fluoride (VDF),perfluoro-2,2-dimethyl-1,3-dioxol (PDD), perfluoro(allyl vinyl ether),perfluoro(butenyl vinyl ether), and the like.

The resin particles of the present invention preferably have an angle ofrepose of 5° or more and 60° or less. As a result, the flowability ofthe resin particles becomes higher, and continuous supply to a moldingmachine or the like is facilitated. The angle of repose is morepreferably 5° or more and 40° or less, and further preferably 10° ormore and 40° or less.

Here, the angle of repose refers to an angle formed by the ridgeline ofa flat surface and a resin powder when the powder is deposited on theflat surface. The angle of repose can be evaluated by filling acontainer with resin powder, letting it fall naturally, and measuringthe angle formed by the resin powder that is piled up when deposited ona horizontal plane. A specific method for measuring the angle of reposewill be described in Examples described hereinbelow.

In the first aspect of the present invention, there is no limitation onthe molecular weight of the resin of the resin particles, and the weightaverage molecular weight measured by gel permeation chromatography (GPC)is, for example, 2,500 to 2,000,000 or the like. From the viewpoint ofthe melt viscosity of the resin and the mechanical strength, the weightaverage molecular weight is preferably 10,000 to 1,000,000 (g/mol). Atthe time of measurement, polymethyl methacrylate is used as a standardsample, and the weight average molecular weight in terms of polymethylmethacrylate is calculated from the elution time of the resin of theresin particles and the standard sample.

Next, a method for producing resin particles according to the firstaspect of the present invention will be described.

The resin particles of the first aspect of the present invention can beproduced, for example, by a method including a step of subjecting amixture of a radical polymerization initiator, a monomer represented bythe following general formula (3), and an organic solvent topolymerization conditions to obtain a resin including a residue unitrepresented by the general formula (4).

In the formula (3), Rf₅, Rf₆, Rf₇, and Rf₈ are the same as Rf₁, Rf₂,Rf₃, and Rf₄, respectively, in the formula (1).

In the formula (4), Rf₅, Rf₆, Rf₇, and Rf₈ are the same as Rf₁, Rf₂,Rf₃, and Rf₄, respectively, in the formula (1).

In the method for producing resin particles of the present invention,the organic solvent dissolves the monomer represented by the generalformula (3), does not dissolve at least a part of the resin includingthe residue unit represented by the general formula (4) generated bypolymerization, and causes precipitation of the resin. The resinproduced by the polymerization precipitates as particles in the organicsolvent. The organic solvent used in the method for producing the resinparticles of the present invention may be referred to as a“precipitation polymerization solvent”. More specifically, theprecipitation polymerization solvent can be an organic solvent thatdissolves the monomer represented by the general formula (3) and doesnot dissolve the resin including the residue unit represented by thegeneral formula (4). This precipitation polymerization solvent ishereinafter referred to as precipitation polymerization solvent A. Inthe present invention, by using a precipitation polymerization solvent,the resin generated by the polymerization reaction can be precipitatedas particles having a specific volume average particle diameter, and asa result, resin particles having excellent moldability and fillingproperty can be produced. Further, since a polymerization aid such as anemulsifier and a dispersant is not used, resin particles that do notcontain an emulsifier and a dispersant that cause a decrease intransparency and heat resistance can be produced.

Here, the precipitation polymerization solvent A means a solvent inwhich resin particles remain after the resin particles including theresidue unit represented by the general formula (4) have been immersedin the organic solvent for a long time. Specifically, the organicsolvent can be regarded as the precipitation polymerization solvent Awhen the remainder of resin particles can be visually confirmed in theorganic solvent after resin particles having a weight average molecularweight Mw of 5×10⁴ to 70×10⁴ and including a residue unit represented bythe general formula (4) have been immersed in the organic solvent at 50°C. for 5 h or more. It is preferable that the precipitationpolymerization solvent A be an organic solvent such that the weight lossratio of a resin sample is less than 20% by weight when the solution iscooled to 25° C. after the immersion at 50° C. for 5 h or more, and thenthe resin sample remaining in a solid state is recovered. The weightloss ratio of the resin sample is more preferably less than 12% byweight, and still more preferably less than 10% by weight.

The loss ratio of resin weight can be measured by the following method.After filtering the above cooled solution with a filter, the solid onthe filter is rinsed with the solvent, washed with acetone a pluralityof times and then dried, and the resin sample on the filter isrecovered. The weight of the recovered resin is measured, and the 100percentage of the value obtained by dividing the value obtained bysubtracting the weight of the recovered resin from the amount of resinimmersed in the organic solvent by the amount of resin immersed in theorganic solvent is taken as the resin loss ratio.

Examples of the precipitation polymerization solvent include non-halogenorganic solvents such as acetone, methyl ethyl ketone, hexane, and butylacetate, chlorine-containing organic solvents such as dichloromethaneand chloroform, and organic solvents including a fluorine atom in themolecule.

Further, as the precipitation polymerization solvent, an organic solventincluding a fluorine atom and a hydrogen atom in the molecule ispreferable because a chain transfer reaction is unlikely to occur inradical polymerization, the polymerization yield is excellent, and ahigh molecular weight substance can be easily obtained. Specificexamples of the precipitation polymerization solvent including fluorineatom and hydrogen atom in the molecule include1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether,2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol,1,2,2,3,3,4,4-heptafluorocyclopentane, 1H,1H-pentafluoropropanol,1H,1H-heptafluorobutanol, 2-perfluorobutylethanol,4,4,4-trifluorobutanol, 1H,1H,3H-tetrafluoropropanol,1H,1H,5H-octafluoropropanol, 1H,1H,7H-dodecafluoroheptanol,1H,1H,3H-hexafluorobutanol, 2,2,3,3,3-pentafluoropropyl difluoromethylether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether,1,1,2,2-tetrafluoroethylethyl ether,1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether,hexafluoroisopropylmethyl ether,1,1,3,3,3-pentafluoro-2-trifluoromethylpropylmethyl ether,1,1,2,3,3,3-hexafluoropropylmethyl ether,1,1,2,3,3,3-hexafluoropropylethyl ether,2,2,3,4,4,4-hexafluorobutyldifluoromethyl ether, and the like.

Among them, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether,2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, and1,2,2,3,3,4,4-heptafluorocyclopentane are preferable, and 1,2,2,3,3,44-heptafluorocyclopentane is preferred since the polymerization yield isexcellent and a high molecular weight substance can be easily obtained.The ratio of fluorine atoms and hydrogen atoms in the molecule of theprecipitation polymerization solvent is preferably fluorineatoms:hydrogen atoms=1:9 to 9:1, more preferably 1:9 to 7:3, and evenmore preferably 4:6 to 7:3 in terms of the number of atoms, because thepolymerization yield is excellent.

The precipitation polymerization solvent preferably includes a fluorineatom and a hydrogen atom in the molecule because an excellentpolymerization yield is obtained, and the amount of the hydrogen atom inthe solvent is preferably 1% by weight or more, and more preferably 1.5%by weight or more based on the weight of the solvent molecule. Further,the amount of the hydrogen atom in the solvent is preferably 1% byweight or more and 5% by weight or less, and preferably 1.5% by weightor more and 4% by weight or less since the polymerization yield isexcellent and a high molecular weight substance can be easily obtained.Moreover, the precipitation polymerization solvent preferably does notinclude a chlorine atom in the molecule since the polymerization yieldis excellent and a high molecular weight substance can be easilyobtained.

As for the ratio of the monomer represented by the general formula (3)to the precipitation polymerization solvent, the monomer:precipitationpolymerization solvent ratio, in terms of weight ratio, is preferably1:99 to 50:50, more preferably 5:95 to 40:60, and even more preferably5:95 to 30:70 because excellent productivity is achieved and particleshaving excellent flow characteristics can be obtained.

Examples of the radical polymerization initiator for performing radicalpolymerization include organic peroxides such as benzoyl peroxide,lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tetr-butylperoxide, tetr-butylcumyl peroxide, and dicumyl peroxide, tetr-butylperoxyacetate, perfluoro(di-tetr-butyl peroxide),bis(2,3,4,5,6-pentafluorobenzoyl) peroxide, and tetr-butylperoxybenzoate, and tetr-butyl perpivalate; and azo-based initiatorssuch as 2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2-butyronitrile), 2,2′-azobisisobutyronitrile,dimethyl-2,2′-azobisisobutyrate, and1,1′-azobis(cyclohexane-1-carbonitrile).

In the production method of the present invention, it is preferable thatthe monomer represented by the general formula (3) beperfluoro(4-methyl-2-methylene-1,3-dioxolane) represented by the generalformula (5), and the residue unit represented by the general formula (4)be a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unitrepresented by the general formula (6).

Since the resin particles of the present invention are resin particlesthat are unlikely to foam during molding, the amount of weight loss inheating at 250° C. is preferably 1% by weight or less, and preferably0.5% by weight or less. Further, the minimum amount of weight loss inheating at 250° C. is not particularly limited, and can be exemplifiedby 0.001% by weight or more. Further, since the resin particles of thepresent invention are resin particles that are unlikely to foam duringmolding, the residual solvent amount contained in the resin ispreferably 1% by weight or less, and preferably 0.5% by weight or less.Here, the amount of weight loss in heating at 250° C. indicates theamount of weight loss at 250° C. when the temperature is raised from 40°C. at 10° C./min under an air stream using TG-DTA and is found from(1−(sample weight at 250° C.)/(weighed sample weight))×100).

The second aspect of the present invention will be described in detailbelow.

The second aspect of the present invention relates to a fluororesinincluding a residue unit represented by the following general formula(1), in which a weight average molecular weight Mw is in the range of5×10⁴ to 3×10⁵, and a yellow index of a heat-melted molded product(thickness of 3 mm) after heating for 24 h at 280° C. is 6 or less.

In the formula (1), Rf₁, Rf₂, Rf₃, and Rf₄ are each independently one ofthe groups consisting of a fluorine atom, a linear perfluoroalkyl grouphaving 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbonatoms. The perfluoroalkyl group may have an ethereal oxygen atom.Further, Rf₁, Rf₂, Rf₃, and Rf₄ may be linked to one another to form aring having 4 or more and 8 or less carbon atoms, and the ring mayinclude an ethereal oxygen atom.

The second aspect of the present invention is a fluororesin including aresidue unit represented by the specific general formula (1). Since thefluororesin of the present invention has a bulky ring structure includedin the specific general formula (1), the fluororesin is amorphous andhas high transparency and high heat resistance. Moreover, since thefluororesin is composed only of carbon, fluorine and oxygen, thefluororesin has high electrical properties, chemical resistance,waterproofness and liquid-repellent oil-repellent property.

The Rf₁, Rf₂, Rf₃, and Rf₄ groups in the residual unit represented bythe general formula (1) in the second aspect of the present inventionare each independently one of the group consisting of a fluorine atom, alinear perfluoroalkyl group having 1 to 7 carbon atoms, a branchedperfluoroalkyl group having 3 to 7 carbon atoms, or a cyclicperfluoroalkyl group having 3 to 7 carbon atoms. The perfluoroalkylgroup may have an ethereal oxygen atom. Further, Rf₁, Rf₂, Rf₃, and Rf₄may be linked to one another to form a ring having 4 or more and 8 orless carbon atoms, and the ring may include an ethereal oxygen atom.

Examples of the linear perfluoroalkyl group having 1 to 7 carbon atomsinclude a trifluoromethyl group, a pentafluoroethyl group, aheptafluoropropyl group, a nonafluorobutyl group, an undecafluoropentylgroup, a tridecafluorohexyl group, and a pentadecafluoroheptyl group;examples of the branched perfluoroalkyl group having 3 to 7 carbon atomsinclude a heptafluoroisopropyl group, a nonafluoroisobutyl group, anonafluorosec-butyl group, and a nonafluorotert-butyl group; andexamples of the cyclic perfluoroalkyl group having 3 to 7 carbon atomsinclude a heptafluorocyclopropyl group, a nonafluorocyclobutyl group,and a tridecafluorocyclohexyl group. Examples of the linearperfluoroalkyl group which has 1 to 7 carbon atoms and may have anethereal oxygen atom include a —CF₂OCF₃ group, a-(CF₂)₂OCF₃ group, and a—(CF₂)₂OCF₂CF₃ group; examples of the cyclic perfluoroalkyl group whichhas 3 to 7 carbon atoms and may have an ethereal oxygen atom include a2-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, a4-(2,3,3,4,4,5,5,6,6-decafluoro)-pyrinyl group, and a2-(2,3,3,4,4,5,5-heptafluoro)-furanyl group.

From the viewpoint of showing excellent heat resistance, it ispreferable that at least one of Rf₁, Rf₂, Rf₃ and Rf₄ be one of thegroup consisting of a linear perfluoroalkyl group having 1 to 7 carbonatoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, and acyclic perfluoroalkyl group having 3 to 7 carbon atoms.

Specific examples of the residue unit represented by the general formula(1) include the residue units shown hereinbelow.

Among these, a fluororesin including a residue unit represented by thefollowing formula (2) is preferable because of excellent heat resistanceand molding processability thereof, and a fluororesin includingperfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit is morepreferable.

The fluororesin of the second aspect of the present invention has aweight average molecular weight Mw in the range of 5×10⁴ to 3×10⁵. Whenthe weight average molecular weight Mw is in this range, the meltviscosity at a shear rate of 10⁻² s and 250° C. can be 1×10² to 3×10⁵Pa·s, and as a result, the melt molding processability is excellent.Furthermore, excellent defoaming property at the time of melting is alsoachieved. Further, when the weight average molecular weight Mw is inthis range, cracks are less likely to occur during heating and cooling.From the viewpoint of excellent melt molding processability andexcellent defoaming property at the time of melting, the fluororesin ofthe present invention preferably has a weight average molecular weightMw in the range of 5×10⁴ to 2×10⁵, because where the weight averagemolecular weight Mw is within this range, the melt viscosity at a shearrate of 10⁻² s and 250° C. can be 1×10² to 2×10⁴ Pa·s, and as a result,the melt molding processability is excellent and the defoaming propertyis also excellent. From the viewpoint of excellent melt moldingprocessability and defoaming property at the time of melting, the weightaverage molecular weight Mw is more preferably in the range of 5×10⁴ to1.5×10⁵, and from the viewpoint of obtaining less cracking duringheating and cooling, the range is more preferably 6×10⁴ to 1.5×10⁵.

The weight average molecular weight Mw of the fluororesin according tothe second aspect of the present invention can be calculated from theelution time of a sample and a standard sample and the molecular weightof the standard sample by using gel permission chromatography (GPC) andusing, for example, standard polymethyl methacrylate having a knownmolecular weight as a standard sample, and using solvent capable ofdissolving both the standard sample and the fluororesin as an eluent.The solution can be prepared by adding 1,1,1,3,3,3-hexafluoro-2-propanol(manufactured by Wako Pure Chemical Industries, Ltd.) to ASAHIKLINAK-225 (manufactured by Asahi Glass Co., Ltd.) at 10% by weight withrespect to AK-225.

The molecular weight distribution Mw/Mn, which is the ratio of theweight average molecular weight Mw to the number average molecularweight Mn, of the fluororesin according to the second aspect of thepresent invention is not particularly limited, but from the viewpoint ofsuppressing yellowing after heating and melting and achieving excellentmelt molding processability, excellent defoaming property duringmelting, and less cracking during heating and cooling, the molecularweight distribution Mw/Mn is preferably 1.2 to 8, more preferably 1.2 to5, even more preferably 1.5 to 3, and even more preferably 2.0 to 3. Thenumber average molecular weight Mn can be measured by the same method asthe above-mentioned method for measuring the weight average molecularweight Mw, and the molecular weight distribution Mw/Mn can be calculatedby dividing the weight average molecular weight Mw by the number averagemolecular weight Mn.

The fluororesin of the second aspect of the present invention has ayellow index of a heat-melted molded product (thickness 3 mm) after 24 hat 280° C. of 6 or less. The yellow index of the heat-melted moldedproduct (thickness 3 mm) after 24 h at 280° C. is preferably 5 or less,more preferably 4 or less, and even more preferably 3 or less. A yellowindex of a heat-melted molded product (thickness 3 mm) after 24 h at280° C. is as follows.

A total of 2.0 g of fluororesin was weighed into a Petri dish with aninner diameter of 26.4 mm (only a receiver in a set including a lid anda receiver in a flat Petri dish manufactured by Flat Co., Ltd., a glassthickness of 1 mm at the bottom), the Petri dish was placed in an inertoven (DN4111, manufactured by Yamato Scientific Co., Ltd.) and allowedto stand at room temperature for 30 min under an air stream (20 L/min),and the temperature was then raised to 280° C. over 30 min, followed byheating at 280° C. for 24 h. After that, the power of the inert oven wasturned off while the oven door was closed and the air flow wasmaintained (20 L/min), and the sample was naturally cooled for 12 h andtaken out. As a result, a fluororesin heat-melted molded product havinga thickness of 3 mm and a diameter of 26.4 mm was obtained on the Petridish. At this time, air compressed by a compressor and passed through adehumidifier (dew point temperature −20° C. or lower) was used as theair. The transmittance was measured at each wavelength at 1 nm intervalsat wavelengths of 200 nm to 1500 nm using a spectrophotometer (U-4100,manufactured by Hitachi High-Tech Science Co., Ltd.) for each obtainedfluororesin heat-melted molded product together with the Petri dish.Data at 5 nm intervals at wavelengths of 380 nm to 780 nm were extractedfrom the measured transmittance data, and the tristimulus values X, Y,and Z of the XYZ color system were calculated according to the method ofJIS Z8701, the yellow index (YI) under a C light source (auxiliaryilluminant C) was calculated according to the method of JIS K7373, andthe yellow index (YI) of the fluororesin heat-melted molded productincluding the Petri dish was obtained. The yellow index (YI) of thePetri dish (receiver only) alone was measured, and the yellow index (YI)of the Petri dish (receiver only) was subtracted from the yellow index(YI) of the fluororesin molded product including the Petri dish toobtain the yellow index (YI) of the fluororesin heat-melted moldedproduct having a size of 3 mm. The yellow index (YI) of the Petri dishalone (receiver only) was 0.21.

Generally, lowering the molecular weight is effective for lowering themelt viscosity, but there is a problem that lowering the molecularweight lowers the glass transition temperature. The fluororesinaccording to the second aspect of the present invention preferably has aglass transition temperature of 125° C. or higher and 145° C. or lowereven though the weight average molecular weight is in the above range.The fluororesin of the second aspect of the present invention preferablyhas a glass transition temperature of 125° C. or higher and 140° C. orlower, more preferably 128° C. or higher and 140° C. or lower, andfurther preferably 129° C. or higher and 135° C. or lower.

The glass transition temperature of the fluororesin of the second aspectof the present invention can be measured by determining the intermediateglass transition temperature using a differential scanning calorimeter(DSC). The measurement conditions can be exemplified by placing a samplein an aluminum sample pan, and raising the temperature the first time as−80° C.→200° C.→−80° C. (heating rate: 10° C./min) and the second timeas −80° C.→200° C. (heating rate: 10° C./min) under a nitrogen stream(500 mL/min). The glass transition temperature can be calculated bydetermining the intermediate glass transition temperature according tothe description of JIS-K 7121 from the chart obtained during secondtemperature rising. In this case, the DSC apparatustemperature-calibrated with indium and tin as standard substances can beused.

From the viewpoints of excellent melt molding processability anddefoaming property during melting, less cracking during heating andcooling, and suppression of yellowing after heating and melting, it ispreferable that the fluororesin of the second aspect of the presentinvention have a melt viscosity of 1×10² Pa·s to 3×10⁵ Pa·s at a shearrate of 10⁻² s and at 250° C. From the viewpoints of excellent meltmolding processability and defoaming property during melting, lesscracking during heating and cooling, and suppression of yellowing afterheating and melting, the melt viscosity is more preferably in the rangeof 1×10² Pa·s to 5×10⁴ Pa·s, even more preferably in the range of 1×10³Pa·s to 5×10⁴ Pa·s, and further preferably in the range of 1×10³ Pa·s to2×10⁴ Pa·s. As a method for measuring the melt viscosity, for example,measurement by a commercially available rotary rheometer can beexemplified, and the method described in JIS K 7244-10 can beexemplified.

From the viewpoint of good heat moldability, it is preferable that inthe fluororesin of the second aspect of the present invention, the areaoccupied by bubbles in the heat-melted molded product (thickness 3 mm,diameter 26.4 mm) at 280° C. for 24 h be 10% or less of the area of themolded product. The area occupied by the bubbles in the heat-meltedmolded product (thickness 3 mm, diameter 26.4 mm) heated at 280° C. for24 h is 5% or less, and more preferably 0%, with respect to the area ofthe molded product. Here, the ratio of the area occupied by the bubblesin the heat-melted molded product (thickness 3 mm, diameter 26.4 mm)heated at 280° C. for 24 h to the area of the molded product can bevisually determined when it is visually clear. It can also be obtainedby capturing an image of the molded product and analyzing it with imageanalysis software or the like.

From the viewpoint of good heat moldability, it is preferable that inthe fluororesin of the second aspect of the present invention, thenumber of bubbles in the heat melt molded product (thickness 3 mm,diameter 26.4 mm) at 280° C. for 24 h be 10 or less. The number ofbubbles in the melt-molded product (thickness 3 mm, diameter 26.4 mm)heated at 280° C. for 24 h is preferably 5 or less, and more preferably0.

From the viewpoint of having excellent heat resistance, it is preferablethat in the fluororesin according to the second aspect of the presentinvention, the difference B−A between an amount A of weight lossimmediately after the temperature was raised to 300° C. at 10° C./min inair in TG-DTA and an amount B of weight loss after the temperature wasraised to 300° C. and then held at 300° C. for 30 min be 1.0% or less.More preferably, the difference B−A is 0.5% or less, and even morepreferably 0.3% or less. Here, the amount A (% by weight) of weight lossimmediately after the temperature was raised to 300° C. is obtained by(sample weight immediately after the temperature was raised to 300°C.)/(weighed sample weight)×100, and the amount B (% by weight) ofweight loss after the temperature was raised to 300° C. and then held at300° C. for 30 min is obtained by (sample weight after the temperaturewas raised to 300° C. and then held at 300° C. for 30 min)/(weighedsample weight)×100.

The fluororesin of the second aspect of the present invention mayinclude other monomer residue units, and examples of the other monomerresidue units include tetrafluoroethylene (TFE), hexafluoropropylene(HFP), chlorotrifluoroethylene (CTFE), trifluoroethylene,hexafluoroisobutylene, a perfluoroalkylethylene, a fluorovinyl ether,vinyl fluoride (VF), vinylidene fluoride (VDF),perfluoro-2,2-dimethyl-1,3-dioxole (PDD), perfluoro(allyl vinyl ether),perfluoro(butenyl vinyl ether), and the like.

Next, a method for producing the fluororesin according to the secondaspect of the present invention will be described.

The fluororesin according to the second aspect of the present inventioncan be produced by a method including a step of polymerizing a monomerrepresented by the following general formula (3) in the presence of aradical polymerization initiator and a chain transfer agent to obtain afluororesin including a residual unit represented by the followinggeneral formula (4), the method using an organic compound having 1 to 20carbon atoms including at least one atom selected from the groupconsisting of a hydrogen atom and a chlorine atom as the chain transferagent. As a result, the obtained fluororesin has a weight averagemolecular weight Mw in the range of 5×10⁴ to 3×10⁵, and the yellow indexof the heat-melted molded product (thickness 3 mm) at 280° C. for 24 his 6 or less.

In the formula (3), Rf₆, Rf₆, Rf₇, and Rf₈ independently show at leastone selected from the group consisting of a fluorine atom, a linearperfluoroalkyl group having 1 to 7 carbon atom, a branchedperfluoroalkyl group having 3 to 7 carbon atoms, and a cyclicperfluoroalkyl group having 3 to 7 carbon atoms, the perfluoroalkylgroup may have an ethereal oxygen atom, Rf₅, Rf₆, Rf₇, and Rf₈ may belinked to one another to form a ring having 4 or more and 8 or lesscarbon atoms, and the ring may be a ring including an ethereal oxygenatom.

In the formula (4), Rf₅, Rf₆, Rf₇, and Rf₈ independently show at leastone selected from the group consisting of a fluorine atom, a linearperfluoroalkyl group having 1 to 7 carbon atom, a branchedperfluoroalkyl group having 3 to 7 carbon atoms, and a cyclicperfluoroalkyl group having 3 to 7 carbon atoms, the perfluoroalkylgroup may have an ethereal oxygen atom, Rf₅, Rf₆, Rf₇, and Rf₈ may belinked to one another to form a ring having 4 or more and 8 or lesscarbon atoms, and the ring may be a ring including an ethereal oxygenatom.

Rf₅, Rf₆, Rf₇, and Rf₈ in the formulas (3) and (4) are the same as Rf₁,Rf₂, Rf₃, and Rf₄ in the formulas (1) and (2) in the second aspect ofthe present invention, respectively.

In the method for producing a fluororesin according to the second aspectof the present invention, by using an organic compound having at leastone atom selected from the group consisting of a hydrogen atom and achlorine atom and having 1 to 20 carbon atoms as the chain transferagent, it is possible to control the molecular weight of the fluororesinwithin the above range while suppressing yellowing after heating andmelting. Here, the chain transfer agent represents a substance having aneffect of lowering the molecular weight by being present in the systemduring radical polymerization of the fluororesin. Specific examples ofthe chain transfer agent include organic compounds having 1 to 20 carbonatoms and including a hydrogen atom, such as toluene, acetone, ethylacetate, tetrahydrofuran, methyl ethyl ketone, methanol, ethanol, andisopropanol; and organic compounds having 1 to 20 carbon atoms andincluding a chlorine atom, such as chloroform, dichloromethane,tetrachloromethane, chloromethane, dichloroethane, trichloroethane,tetrachloroethane, pentachloroethane, hexachloroethane, benzyl chloride,pentafluorobenzyl chloride, and pentafluorobenzoyl chloride. Among them,from the viewpoint of enabling control of the molecular weight of thefluororesin, achieving excellent molding processability, excellentdefoaming property during melting, less cracking during heating andcooling, and also high yield while suppressing yellowing after heatingand melting, an organic compound having 1 to 20 carbon atoms andincluding a chlorine atom is preferable, and a more preferable compoundis represented by the general formula (A).

In the formula (A), m is an integer of 0 to 3, n is an integer of 1 to3, p is an integer of 0 to 1, q is an integer of 0 to 1, and m+n+p+q is4. R¹ and R² are each independently a hydrocarbon group having 1 to 19carbon atoms or an oxygen atom, and the oxygen atom may form a doublebond with an adjacent carbon atom. The total number of carbon atoms ofR¹ and R² is 1 to 19, and the hydrocarbon group may have one or moreatoms selected from an oxygen atom, a fluorine atom, and a chlorineatom, and may have no hydrogen atom. Further, the hydrocarbon group maybe linear, branched, alicyclic or aromatic, and R¹ and R² may be linkedto each other to form a ring having 3 to 19 carbon atoms.

Among them, from the viewpoint of enabling control of the molecularweight of the fluororesin, achieving excellent molding processability,excellent defoaming property during melting, less cracking duringheating and cooling, and also high yield while suppressing yellowingafter heating and melting, an organic compound having 1 to 20 carbonatoms and including a hydrogen atom a chlorine atom is preferable.Examples of the organic compound having 1 to 20 carbon atoms andincluding a hydrogen atom a chlorine atom include chloroform,dichloromethane, chloromethane, dichloroethane, trichloroethane,tetrachloroethane, pentachloroethane, benzyl chloride, pentafluorobenzylchloride, and the like. Further, from the viewpoint of enabling controlof the molecular weight of the fluororesin, achieving excellent moldingprocessability, excellent defoaming property during melting, lesscracking during heating and cooling, and also high yield whilesuppressing yellowing after heating and melting, in the organic compoundhaving 1 to 20 carbon atoms and including a hydrogen atom a chlorineatom, the number ratio of hydrogen atoms to chlorine atoms is preferablyin the range of hydrogen atoms:chlorine atoms=1:9 to 9:1, and morepreferably in the range of 1:9 to 5:5. In addition, from the viewpointof enabling control of the molecular weight of the fluororesin,achieving excellent molding processability, excellent defoaming propertyduring melting, less cracking during heating and cooling, and also highyield while suppressing yellowing after heating and melting, the organiccompound having 1 to 20 carbon atoms and including a hydrogen atom achlorine atom is preferably represented by the following general formula(B) or (C), and more preferably by the general formula (B).

In the formula (B), m and n are independently integers of 1 to 3, p isan integer of 0 to 1, q is an integer of 0 to 1, and m+n+p+q is 4. R¹and R² are each independently a hydrocarbon group having 1 to 19 carbonatoms, and the total number of carbon atoms of R¹ _(p) and R² _(q) is 0to 19, and the hydrocarbon group may have one or more atoms selectedfrom an oxygen atom, a fluorine atom, and a chlorine atom, and may haveno hydrogen atom. Further, the hydrocarbon group may be linear,branched, alicyclic or aromatic, and R¹ and R² may be linked to eachother to form a ring having 3 to 19 carbon atoms.

In the formula (C), m, n, u, and v are each independently an integer of0 to 3, m+u is 1 to 5, n+v is 1 to 5, and p, q, r, s, and t are eachindependently an integer of 0 to 1, m+n+p+q is 3, r+s+u+v is 3, R¹, R²,R³, R⁴, and R⁵ are each independently a hydrocarbon group having 1 to 18carbon atoms, the total number of carbon atoms of R¹, R², R³, R⁴, and R⁵is 0 to 18, and the hydrocarbon group may have one or more atomsselected from oxygen atom, fluorine atom, and chlorine atom, and mayhave no hydrogen atom. Further, the hydrocarbon group may be linear,branched, alicyclic or aromatic, and two or more groups selected fromR¹, R², R³, R⁴, and R⁵ may be linked to each other to form a ring having3 to 19 carbon atoms, and there may be a plurality of such rings.

Examples of the organic compound having 1 to 20 carbon atoms andincluding a chlorine atom that is represented by the general formula (A)include chloroform, dichloromethane, tetrachloromethane, chloromethane,dichloroethane, trichlorethylene, tetrachloroethane, pentachloroethane,hexachloroethane, benzyl chloride, pentafluorobenzyl chloride,pentafluorobenzoyl chloride, and the like. Examples of the organiccompound having 1 to 20 carbon atoms and including a hydrogen atom and achlorine atom that is represented by the general formula (B) includechloroform, dichloromethane, chloromethane, dichloroethane,trichloroethane, tetrachloroethane, pentachloroethane, benzyl chloride,pentafluorobenzyl chloride, and the like. Examples of the organiccompound having 1 to 20 carbon atoms and including a hydrogen atom and achlorine atom that is represented by the general formula (C) include1,1,1-trichloroethane and the like.

Further, a fluororesin having both defoaming property at the time ofmelting and crack resistance, and also excellent defoaming property atthe time of melting and heat resistance, low melt viscosity, and lesscrack generation can be obtained, and the yield is also excellent.Therefore, the amount of the chain transfer agent is preferably 3% byweight to 50% by weight, more preferably 3% by weight to 30% by weight,and even more preferably 4% by weight to 20% by weight, based on thetotal amount of the monomer and the chain transfer agent.

From the viewpoint of obtaining excellent melt molding processability,excellent defoaming property during melting, less cracking duringheating and cooling, and also excellent yield while suppressing yellowduring heating and melting, in the method for producing a fluororesinaccording to the second aspect of the present invention, it ispreferable to use an organic solvent for (hereinafter, referred to as“precipitation polymerization solvent”) that dissolves a monomerrepresented by the general formula (4) and causes precipitation of thefluororesin including a residue unit represented by the general formula(5) as a polymerization solvent.

In the method for producing a fluororesin according to the second aspectof the present invention, it is preferable to select an organic solventhaving a certain specific polarity range as the precipitationpolymerization solvent on the basis of Hansen solubility parameters.

Hansen divided a solubility parameter introduced by Hildebrand intothree components, namely, a dispersion term δD, a polarity term δP, anda hydrogen bond term δH, and these Hansen solubility parameters areshown in a three-dimensional space. The dispersion term δD shows theeffect due to the dispersion forces, the polarity term δP shows theeffect due to the dipole force, and the hydrogen bond term δH shows theeffect due to the hydrogen bond force. The farther the coordinates of acertain resin and the coordinates of a certain organic solvent are inthe three-dimensional space, the more unlikely it is that the resin willdissolve in the organic solvent.

The definition and calculation method of the Hansen solubilityparameters are described in the following document. Charles M. Hansen,“Hansen Solubility Parameters: A Users Handbook”, CRC Press, 2007. Fororganic solvents for which literature values are unknown, the Hansensolubility parameter can be easily estimated from the chemical structureby using computer software (Hansen Solubility Parameters in Practice(HSPiP)).

In the present invention, HSPiP 5th Edition is used, for the organicsolvents registered in the database, the values thereof are used, andfor the organic solvents that are not registered, the estimated value isused.

The Hansen solubility parameters of a resin can be determined bychecking whether the resin precipitates when a solution of the resin ina good solvent is added to a number of different organic solvents forwhich the Hansen solubility parameters have been established.Specifically, when the coordinates of the Hansen solubility parametersof all the organic solvents used in the test are shown in thethree-dimensional space, a sphere (solubility sphere) is found such thatall the coordinates of the organic solvents in which the resin A doesnot precipitate are contained inside a sphere, and the coordinates ofthe organic solvents that cause the precipitation of the resin A areoutside the sphere, and the center coordinate of the solubility sphereis taken as the Hansen solubility parameter of the resin.

In the case where the coordinates of the Hansen solubility parameters ofa certain organic solvent that was not used in the solubility test are(δD, δP, δH), where the coordinates are contained inside the solubilitysphere, it is considered that the organic solvent dissolves a resinwithout causing precipitation. Meanwhile, where the coordinates areoutside the solubility sphere, the organic solvent is considered tocause the precipitation of the resin.

In the present invention, Hansen solubility parameters of a compoundrepresented by a following general formula (7) hereinbelow (the pentamerof the compound represented by the general formula (4)) that wereestimated using HSPiP were used as the Hansen solubility parameter ofthe resin particles. By this method, for example, the Hansen solubilityparameters (δD, δP, δH of the resin particles including theperfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit representedby the general formula (2) are 11.6, 3.5, and 1.4 (MPa^(1/2)),respectively.

In the formula (7), Rf₉, Rf₁₀, Rf₁₁, and Rf₁₂ are each independently atleast one from the group consisting of a fluorine atom, a linearperfluoroalkyl group having 1 to 7 carbon atoms, a branchedperfluoroalkyl group having 3 to 7 carbon atoms, and a cyclicperfluoroalkyl group having 3 to 7 carbon atoms. The perfluoroalkylgroup may have an ethereal oxygen atom. Further, Rf₉, Rf₁₀, Rf₁₁, andRf₁₂ may be linked to one another to form a ring having 4 or more and 8or less carbon atoms, and the ring may be a ring including an etherealoxygen atom.

As the precipitation polymerization solvent in the second aspect of thepresent invention, it is preferable to select an organic solvent havinga dissolution index R with the resin of 4 or more, which is calculatedby a formula (8) from the Hansen solubility parameters.R=4×{(δD ₁ −δD ₂)²+(δP ₁ −δP ₂)²+(δH ₁ −δH ₂)²}^(0.5)  (8)

Here, δD₁, δP₁, and δH₁ are the dispersion term, polarity term andhydrogen term of the Hansen solubility parameters of the resinparticles, respectively, and δD₂, δP₂, and δH₂ are the dispersion term,polarity term and hydrogen term of the Hansen solubility parameters ofthe organic solvent, respectively.

For example, the following organic solvent can be mentioned as anorganic solvent having an affinity Ra of 4 or more with a resinincluding a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit.

TABLE 1 Table 2-1 Literature Solvent type δD δP δH R value Acetone 15.510.4  7.0 11.8 Database value Methyl ethyl ketone 16.0 9.0 5.1 11.0Database value Hexane 14.9 0.0 0.0 7.6 Database value Chloroform 17.83.1 5.7 13.1 Database value Butyl acetate 15.8 3.7 6.3 9.7 Databasevalue Toluene 18.0 1.4 2.0 13.0 Database value 2,2,2-Trifluoroethanol15.4 8.3 16.4 17.5 Database value 1,2,2,3,3,3-Hexafluoro- 17.2 4.5 14.717.4 Database 2-propanol value 1,2,2,3,3,4,4- 14.5 2.7 2.1 5.9Calculated Heptafluorocyclopentane value 1,1,2,2-Tetrafluoroethyl- 14.15.0 4.0 5.8 Calculated 2,2,2-trifluoroethyl ether value

Further, from the viewpoint of suppressing yellowing after heating andmelting and achieving excellent molding processability, excellentdefoaming property during melting, less cracking during heating andcooling, and also high yield, an organic solvent including a fluorineatom and a hydrogen atom in the molecule is preferable as theprecipitation polymerization solvent. Specific examples of theprecipitation polymerization solvent including a fluorine atom and ahydrogen atom in the molecule include1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether,2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol,1,2,2,3,3,4,4-heptafluorocyclopentane, 1H,1H-pentafluoropropanol,1H,1H-heptafluorobutanol, 2-perfluorobutylethanol,4,4,4-trifluorobutanol, 1H,1H,3H-tetrafluoropropanol,1H,1H,5H-octafluoropropanol, 1H,1H,7H-dodecafluoroheptanol,1H,1H,3H-hexafluorobutanol, 2,2,3,3,3-pentafluoropropyldifluoromethylether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether,1,1,2,2-tetrafluoroethyl ethyl ether,1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether,hexafluoroisopropylmethyl ether,1,1,3,3,3-pentafluoro-2-trifluoromethylpropylmethyl ether,1,1,2,3,3,3-hexafluoropropylmethyl ether, 1,1,2,3,3,3-hexafluoropropylethyl ether, 2,2,3,4,5,4-hexafluorobutyldifluoromethyl ether, and thelike.

Among them, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether,2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol and1,2,2,3,3,4,4-heptafluorocyclopentane are preferable, and from theviewpoint of suppressing yellowing after heating and melting andachieving excellent molding processability, excellent defoaming propertyduring melting, less cracking during heating and cooling, and also highyield, 1,2,2,3,3,4,4-heptafluorocyclopentane is preferable. As for theratio of fluorine atoms to hydrogen atoms in the molecule of theprecipitation polymerization solvent, from the viewpoint of suppressingyellowing after heating and melting and achieving excellent moldingprocessability, excellent defoaming property during melting, lesscracking during heating and cooling, and also high yield, the numberratio of atoms is preferably fluorine atoms:hydrogen atoms=1:9 to 9:1.

Whether the organic solvent causes the precipitation of a resinincluding a residue unit represented by the general formula (4) can bedetermined by dropwise adding a solution obtained by dissolving theresin in a good solvent to the organic solvent, and the organic solventis determined to cause the precipitation of the resin in the case wherethe resin precipitates. The good solvent is a solvent that dissolves theresin, and examples thereof include perfluorocarbons such asperfluorohexane and hexafluorobenzene.

Examples of the radical polymerization initiator for performing radicalpolymerization include perfluoroorganic peroxides such asbis(perfluorobenzoyl) peroxide (PFBPO), (CF₃COO)₂, (CF₃CF₂COO)₂,(C₃F₇COO)₂, (C₄F₉COO)₂, (C₅F₁₁COO)₂, (C₆F₁₃COO)₂, (C₇F₁₅COO)₂, and(C₈F₁₇COO)₂; organic peroxides such as benzoyl peroxide, laurylperoxide, octanoyl peroxide, acetyl peroxide, di-tert-butyl peroxide,tert-butyl cumyl peroxide, dicumyl peroxide, tert-butyl peroxyacetate,perfluoro(di-tert-butyl peroxide), bis(2,3,4,5,6-pentafluorobenzoyl)peroxide, tert-butylperoxybenzoate, and tert-butylperpivalate; andazo-based initiators such as 2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2-butyronitrile), 2,2′-azobisisobutyronitrile,dimethyl-2,2′-azobisisobutyrate, and1,1′-azobis(cyclohexane-1-carbonitrile). Among them, from the viewpointof suppressing yellowing after heating and melting and achievingexcellent molding processability, excellent defoaming property duringmelting, and less cracking during heating and cooling, perfluoroorganicperoxides are preferable, and bis (perfluorobenzoyl)peroxide (PFBPO) iseven more preferable. Here, the perfluoroorganic peroxide refers to acompound having a structure in which a hydrogen atom of the organicperoxide is replaced with a fluorine atom.

In the production method of the present invention, the monomerrepresented by the general formula (3) is preferablyperfluoro(4-methyl-2-methylene-1,3-dioxolane) represented by the generalformula (5), and the residue unit represented by the formula (4) ispreferably a perfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unitrepresented by the general formula (6).

In the fluororesin obtained by production by the method of the presentinvention, yellowing after heating and melting is suppressed, excellentmolding processability, excellent defoaming property during melting, andless cracking during heating are achieved, a change in the amount ofweight loss when held at 300° C. for a certain period of time is small,and thermal decomposition is unlikely to occur.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to Examples, but the present invention is not limited to theseExamples.

(Example of First Aspect of Present Invention)

<Volume Average Particle Diameter>

The volume average particle diameter (unit: μm) was measured usingMT3000 manufactured by Microtrac Co., Ltd. and methanol as a dispersionmedium.

<10% Particle Diameter>

The 10% particle diameter (unit: μm) was measured using MT3000manufactured by Microtrac Co., Ltd. and methanol as a dispersion medium.

<90% Particle Diameter>

The 90% particle diameter (unit: μm) was measured using MT3000manufactured by Microtrac Co., Ltd. and methanol as a dispersion medium.

<Flowability>

The case where the shape of the resin was particulate was regarded asgood (A), and the case where it was not particulate was regarded asdefective (B).

<Bulk Density>

Resin particles were dropped and filled up to the 50 mL mark on thegraduated cylinder without impacting the graduated cylinder. The weight(g) of the resin particles per 50 mL of the volume was measured. Thebulk density (g/mL) was calculated by dividing the weight of the resinparticles by the volume.

<Filling Property>

A bulk density of 0.2 g/mL or more was regarded as good (A), and a bulkdensity of less than 0.2 g/mL was regarded as poor (B).

<Weight Average Molecular Weight Mw>

Measurements were performed using a column TSKgel SuperHZM-Mmanufactured by Tosoh Corporation and gel permission chromatographequipped with an RI detector. An eluent was prepared by adding1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Wako Pure ChemicalIndustries, Ltd.) to ASAHIKLIN AK-225 (manufactured by Asahi Glass Co.,Ltd.) in an amount of 10% by weight based on AK-225. Standard polymethylmethacrylate manufactured by Agilent Technologies, Inc. was used as astandard sample, and the weight average molecular weight Mw in terms ofpolymethyl methacrylate was calculated from the elution times of thesample and the standard sample.

<Amount of Weight Loss in Heating at 250° C.>

About 10 mg to 15 mg of a sample was weighed in an aluminum sample pan(SSC000E030, manufactured by Hitachi High-Tech Science Co., Ltd.), thetemperature was raised from 40° C. to 300° C. at 10° C./min under aninstrumented air flow (160 mL/min) in a TG/DTA device (TG/DTA6200AST2,manufactured by Hitachi High-Tech Science Co., Ltd.), and an amount ofweight loss at 250° C. (1−(sample weight at 250° C.)/(weighed sampleweight))×100) was obtained and taken as the amount of weight loss inheating at 250° C.

<Angle of Repose>

A sample bottle was filled with 7 ml of resin powder, a glass powderfunnel (manufactured by AS ONE Corporation, the diameter of the upperpart of the funnel is 50 mm, the diameter of the lower part of thefunnel is 10 mm, the total length of the funnel is 100 mm, the height ofthe funnel foot portion is 40 mm) was fixed on a circular table (made ofglass) with a diameter of 4 cm, so that the lower end of the powderfunnel was 4 cm above the circular table, the funnel was used to dropthe resin powder from the height of the upper end of the funnel, and theangle (°) of the slope of the heap formed by the deposited powder wasmeasured with a protractor (in the comparative example, the flowabilityof the resin powder was poor, so the resin powder was dropped withoutusing the powder funnel).

(Example 1-1) Production ofPerfluoro(4-Methyl-2-Methylene-1,3-Dioxolane) Resin Particles

The inside of a 1 L SUS316 autoclave equipped with an anchor typestirring blade, a nitrogen introduction tube and a thermometer wasreplaced with nitrogen. A total of 1.288 g (0.00305 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 150.0 g(0.615 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane as amonomer, and 1340 g of ASAHIKLIN AE-3000 (manufactured by Asahi GlassCo., Inc., 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, amountof hydrogen atoms in the solvent molecule:1.51% by weight, and fluorineatom:hydrogen atom=7:3 (number ratio) in the solvent molecule) as aprecipitation polymerization solvent were added, and precipitationpolymerization was carried out by holding at 55° C. for 24 h understirring. Perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles(resin A) (yield: 56%) were obtained by cooling to room temperature,filtering off the liquid including purified resin particles, washingwith acetone, and vacuum drying. Table 1-1 shows the shape, volumeaverage particle diameter, 10% particle diameter, 90% particle diameter,bulk density, and angle of repose of the obtained resin particles. Theobtained resin particles were excellent in flowability and fillingproperty. The weight average molecular weight Mw of the obtained resin Awas 4.4×10⁵.

TABLE 2 Table 1-1 Exam- Exam- Exam- ple ple ple Comparative Units 1-11-2 1-3 Example 1-1 Resin — A B C D Shape — Particles ParticlesParticles Indeterminate shape Volume average μm 49 176 117 Measurementparticle diameter is impossible 10% Particle μm 21 73 43 Measurementdiameter is impossible 90% Particle μm 70 308 198 Measurement diameteris impossible Bulk density g/mL 0.32 0.23 0.78 0.06 Angle of repose ° 2030 30 80 Flowability — A A A B Filling property — A A A B Weight lossamount % by 0.05 0.19 0.28 1.36 during heating at weight 250° C.

TABLE 3 Table 1-2 Example Example Units 1-4 1-5 Resin — E F Shape —Particles Particles Volume average particle μm 57 109 diameter 10%Particle diameter μm 21 47 90% Particle diameter μm 82 174 Bulk densityg/mL 0.39 0.26 Angle of repose ° 20 20 Flowability — A A Fillingproperty — A A Weight loss amount during % by 0.04 0.06 heating at 250°C. weight

(Comparative Example 1-1) Production ofPerfluoro(4-Methyl-2-Methylene-1,3-Dioxolane) Resin

A total of 0.017 g (0.0000407 mol) of bis(2,3,4,5,6-pentafluorobenzoyl)peroxide as an initiator, 5.0 g (0.0205 mol) ofperfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, and 8.2 g ofhexafluorobenzene (amount of hydrogen atoms in the solvent molecule:0%by weight, and fluorine atom:hydrogen atom=10:0 (number ratio) in thesolvent molecule) as a polymerization solvent were placed in a glassampoule having a capacity of 75 mL and were sealed under reducedpressure after repeating nitrogen substitution and depressurization.When this ampoule was placed in a thermostat at 55° C. and held for 24 hto carry out radical solution polymerization, a viscous liquid in whichthe resin was dissolved was obtained. After cooling to room temperature,the ampoule was opened, and the resin solution was diluted with 36 g ofhexafluorobenzene for viscosity adjustment to prepare a resin dilutedsolution. A total of 1 L of chloroform was added to a beaker equippedwith an anchor blade, the resin was precipitated by adding the resindiluted solution to the chloroform under stirring, and the precipitatewas vacuum-dried to obtain perfluoro(4-methyl-2-methylene-1,3-dioxolane)resin (resin D) (yield: 61%). The weight average molecular weight Mw ofthe obtained resin D was 3.5×10⁵. The shape, bulk density, and angle ofrepose of the obtained resin are shown in Table 1-1. Since the resin hadindeterminate shape, the volume average particle diameter could not bemeasured. In this case, the obtained resin had problems in flowabilityand filling property.

(Example 1-2) Production ofPerfluoro(4-Methyl-2-Methylene-1,3-Dioxolane) Resin Particles

The inside of a 1 L SUS316 autoclave equipped with an anchor typestirring blade, a nitrogen introduction tube and a thermometer wasreplaced with nitrogen. A total of 0.346 g (0.000820 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 100.0 g(0.410 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as amonomer, and 890 g of 2,2,2-trifluoroethanol (amount of hydrogen atomsin the solvent molecule: 3.03% by weight, and fluorine atom:hydrogenatom=5:5 (number ratio) in the solvent molecule) as a precipitationpolymerization solvent were added, and precipitation polymerization wascarried out by holding at 55° C. for 24 h under stirring.Perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (resin B)(yield: 78%) were obtained by cooling to room temperature, filtering offthe liquid including purified resin particles, washing with acetone, andvacuum drying. Table 1-1 shows the shape, volume average particlediameter, 10% particle diameter, 90% particle diameter, bulk density,and angle of repose of the obtained resin particles. The obtained resinparticles were excellent in flowability and filling property. The weightaverage molecular weight Mw of the obtained resin B was 1.1×10⁵.

(Example 1-3) Production ofPerfluoro(4-Methyl-2-Methylene-1,3-Dioxolane) Resin Particles

The inside of a 1 L SUS316 autoclave equipped with an anchor typestirring blade, a nitrogen introduction tube and a thermometer wasreplaced with nitrogen. A total of 0.519 g (0.00123 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 150.0 g(0.615 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as amonomer, and 1150 g of chloroform as a precipitation polymerizationsolvent were added, and precipitation polymerization was carried out byholding at 55° C. for 24 h under stirring.Perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (resin C)(yield: 19%) were obtained by cooling to room temperature, filtering offthe liquid including purified resin particles, washing with acetone, andvacuum drying. Table 1-1 shows the shape, volume average particlediameter, 10% particle diameter, 90% particle diameter, bulk density,and angle of repose of the obtained resin particles. The obtained resinparticles were excellent in flowability and filling property. The weightaverage molecular weight Mw of the obtained resin C was 7.0×10³.

(Example 1-4) Production ofPerfluoro(4-Methyl-2-Methylene-1,3-Dioxolane) Resin Particles

The inside of a 1 L SUS316 autoclave equipped with an anchor typestirring blade, a nitrogen introduction tube and a thermometer wasreplaced with nitrogen. A total of 1.038 g (0.00246 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 300.0 g(1.23 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as amonomer, and 1200 g of ZEORORA-H (manufactured by Nippon Zeon Co., Ltd,1,2,2,3,3,4,4-heptafluorocyclopentane, amount of hydrogen atoms in thesolvent molecule: 1.55% by weight, and fluorine atom:hydrogen atom=7:3(number ratio) in the solvent molecule) as a precipitationpolymerization solvent were added, and precipitation polymerization wascarried out by holding at 55° C. for 24 h under stirring.Perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (resin E)(yield: 86%) were obtained by cooling to room temperature, filtering offthe liquid including purified resin particles, washing with acetone, andvacuum drying. Table 1-2 shows the shape, volume average particlediameter, 10% particle diameter, 90% particle diameter, bulk density,and angle of repose of the obtained resin particles. The obtained resinparticles were excellent in flowability and filling property. The weightaverage molecular weight Mw of the obtained resin E was 4.9×10⁵.

(Example 1-5) Production ofPerfluoro(4-Methyl-2-Methylene-1,3-Dioxolane) Resin Particles

The inside of a 1 L SUS316 autoclave equipped with an anchor typestirring blade, a nitrogen introduction tube and a thermometer wasreplaced with nitrogen. A total of 0.519 g (0.00123 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 150.0 g(0.615 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as amonomer, and 1340 g 1,1,1,3,3,3-hexafluoroisopropanol (amount ofhydrogen atoms in the solvent molecule: 1.82% by weight, and fluorineatom:hydrogen atom=6:4 (number ratio) in the solvent molecule) as aprecipitation polymerization solvent were added, and precipitationpolymerization was carried out by holding at 55° C. for 24 h understirring. Perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles(resin F) (yield: 59%) were obtained by cooling to room temperature,filtering off the liquid including purified resin particles, washingwith acetone, and vacuum drying. Table 1-2 shows the shape, volumeaverage particle diameter, 10% particle diameter, 90% particle diameter,bulk density, and angle of repose of the obtained resin particles. Theobtained resin particles were excellent in flowability and fillingproperty. The weight average molecular weight Mw of the obtained resin Fwas 7.9×10⁵.

Reference Example 1-1

The resin particles obtained in Example 1-1 were immersed in a tenfoldamount of various solvents at 50° C. for 5 h, and it was visuallyobserved whether the resin particles remained.

The organic solvents in which the residual resin particles were visuallyconfirmed are as follows:

1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether,2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol,1,2,2,3,3,4,4-heptafluorocyclopentane, and chloroform.

Then, after cooling to 25° C. and filtering through a filter, the resinparticles were taken out by rinsing with the solvent, and then the resinparticles were washed twice with a tenfold amount of acetone and vacuumdried, and a recovery rate was determined from the dry weight. Therecovery rate was 90% or more in each case. Further, when the filtrateobtained was distilled off and the solid content in the filtrate wasdetermined, the solid content in the filtrate was less than 10% withrespect to the resin particles used. From the above results, it wasconfirmed that the weight loss ratio of the resin weight was less than10% by weight.

Reference Example 1-2

The resin particles obtained in Example 1-1 were immersed at 50° C. for5 h in a tenfold amount of various solvents described hereinbelow, andit was visually observed whether the resin particles remained.

The organic solvents in which the residual resin particles were not seenwith the naked eye are as follows:

hexafluorobenzene, CF₃CF₂CHCl₂ (amount of hydrogen atom in the solventmolecule: 0.55% by weight, fluorine atom:hydrogen atom in the solventmolecule=8:2 (number ratio))

As a result of visual observation at 50° C., all the solutions weretransparent and almost no turbidity was confirmed. After cooling to 25°C. and filtration through a filter, rinsing the filter with the solventwas performed, the filter was vacuum dried, and the recovery rate wascalculated from the weight increase of the filter. As a result, theweight increase was less than 5% by weight in all cases. From the aboveresults, it was confirmed that the weight loss ratio of the resin afterimmersion in the solvent was 95% by weight or more.

(Example of Second Aspect of Present Invention)

<Methods for Measuring Physical Properties>

(1) Weight Average Molecular Weight Mw, Molecular Weight DistributionMw/Mn

Measurements were performed using a column TSKgel SuperHZM-Mmanufactured by Tosoh Corporation and gel permission chromatographequipped with an RI detector. An eluent was prepared by adding1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Wako Pure ChemicalIndustries, Ltd.) to ASAHIKLIN AK-225 (manufactured by Asahi Glass Co.,Ltd.) in an amount of 10% by weight based on AK-225. Standard polymethylmethacrylate manufactured by Agilent Technologies, Inc. was used as astandard sample, and the weight average molecular weight Mw and thenumber average molecular weight Mn in terms of polymethyl methacrylatewere calculated from the elution times of the sample and the standardsample. The molecular weight distribution Mw/Mn was calculated bydividing the weight average molecular weight Mw by the number averagemolecular weight Mn.

(2) Glass Transition Temperature

About 10 mg of a sample was weighed in an aluminum sample pan (52-023P,manufactured by Hitachi High-Tech Science Corporation), and the samplewas covered with an aluminum lid (52-023C, manufactured by HitachiHigh-Tech Science Corporation), and sealed with an electric samplesealer (DICE) (manufactured by Hitachi High-Tech Science Corporation)(Hitachi High-Tech Science Corporation). The temperature was raised witha DSC device (DSC6220, manufactured by Hitachi High-Tech ScienceCorporation) by the following program: the first time: −80° C.→200°C.→−80° C. (heating rate: 10° C./min), the second time: −80° C.→200° C.(heating rate: 10° C./min), under a nitrogen stream (500 mL/min). Theglass transition temperature was calculated by determining theintermediate glass transition temperature according to the descriptionof JIS-K7121 from the chart at the time of heating. Further, the DSCapparatus used was temperature-calibrated with indium and tin asstandard substances.

(3) Melt Viscosity

The complex viscosity at a frequency of 10⁻² (rad·s⁻¹) was measured at250° C. by using a rotary rheometer MCR-300 manufactured by Anton-PaarGmbH, and the value of the complex viscosity was expressed as the meltviscosity.

(4) Weight Loss

Approximately 10 mg to 15 mg of a sample was weighed in an aluminumsample pan (SSC000E030, manufactured by Hitachi High-Tech ScienceCorporation), the temperature was raised from 40° C. to 300° C. at 10°C./min under an air flow (160 mL/min) using a TG/DTA device(TG/DTA6200AST2 manufactured by Hitachi High-Tech Science Corporation),and a difference B−A between an amount A of weight loss immediatelyafter the temperature was raised to 300° C. at 10° C./min in air and anamount B of weight loss after the temperature was raised to 300° C. andthen held at 300° C. for 30 min in TG-DTA was determined. Here, theamount A (% by weight) of weight loss immediately after the temperaturewas raised to 300° C. is obtained by (sample weight immediately afterthe temperature was raised to 300° C.)/(weighed sample weight)×100, andthe amount B (% by weight) of weight loss after the temperature wasraised to 300° C. and then held at 300° C. for 30 min is obtained by(sample weight after the temperature was raised to 300° C. and then heldat 300° C. for 30 min)/(weighed sample weight)×100. At this time, aircompressed by a compressor was passed through a dehumidifier (dew pointtemperature −20° C. or lower) was used as the air.

(5) Defoaming Property

A total of 2.0 g of fluororesin was weighed into a Petri dish with aninner diameter of 26.4 mm (only a receiver in a set including a lid andthe receiver in a flat Petri dish manufactured by Flat Co., Ltd., aglass thickness of 1 mm at the bottom), the Petri dish was placed in aninert oven (DN4111, manufactured by Yamato Scientific Co., Ltd.) andallowed to stand at room temperature for 30 min under an air stream (20L/min), and the temperature was then raised to 280° C. over 30 min,followed by heating at 280° C. for 24 h. After that, the power of theinert oven was turned off while the oven door was closed and the airflow was maintained (20 L/min), the sample was naturally cooled for 12h, and taken out. As a result, a fluororesin heat-melted molded producthaving a thickness of 3 mm and a diameter of 26.4 mm was obtained on thePetri dish. At this time, air compressed by a compressor was passedthrough a dehumidifier (dew point temperature −20° C. or lower) was usedas the air.

The appearance of the fluororesin heat-melted molded product (thickness3 mm, diameter 26.4 mm) was observed, the number of bubbles was counted,and the ratio of the area occupied by the bubbles to the area of themolded product was calculated and evaluated according to the followingcriteria.

-   -   A: 0 bubbles    -   B: 1 to 10 bubbles and the area occupied by the bubbles is 10%        or less of the area of the molded product    -   C: 11 or more bubbles and the area occupied by the bubbles is        10% or less of the area of the molded product    -   D: 1 to 10 bubbles and the area occupied by the bubbles is 11%        or more of the area of the molded product    -   E: 11 or more bubbles and the area occupied by the bubbles is        11% to 69% of the area of the molded product    -   F: 11 or more bubbles and the area occupied by the bubbles is        70% or more of the total area of the molded product

(6) Cracks after Heating at 280° C., Melting and Cooling

A total of 2.0 g of fluororesin was weighed into a Petri dish with aninner diameter of 26.4 mm (only a receiver in a set including a lid andthe receiver in a flat Petri dish manufactured by Flat Co., Ltd., aglass thickness of 1 mm at the bottom), the Petri dish was placed in aninert oven (DN4111, manufactured by Yamato Scientific Co., Ltd.) andallowed to stand at room temperature for 30 min under an air stream (20L/min), and the temperature was then raised to 280° C. over 30 min,followed by heating at 280° C. for 24 h. After that, the power of theinert oven was turned off while the oven door was closed and the airflow was maintained (20 L/min), the sample was naturally cooled for 12h, and taken out. As a result, a fluororesin heat-melted molded producthaving a thickness of 3 mm and a diameter of 26.4 mm was obtained on thePetri dish. At this time, air compressed by a compressor was passedthrough a dehumidifier (dew point temperature −20° C. or lower) was usedas the air.

The appearance of the fluororesin heat-melted molded product (thickness3 mm, diameter 26.4 mm) was observed, the number of cracks was counted,and the evaluation was made according to the following criteria.

-   -   A: 3 cracks or less    -   B: 4 to 10 cracks    -   C: 11 to 49 cracks    -   D: 50 or more cracks

(7) Yellow Index (YI) of Heat-Melted Molded Product (Thickness 3 mm) at280° C. for 24 h.

A total of 2.0 g of fluororesin was weighed into a Petri dish with aninner diameter of 26.4 mm (only a receiver in a set including a lid andthe receiver in a flat Petri dish manufactured by Flat Co., Ltd., aglass thickness of 1 mm at the bottom), the Petri dish was placed in aninert oven (DN4111, manufactured by Yamato Scientific Co., Ltd.) andallowed to stand at room temperature for 30 min under an air stream (20L/min), and the temperature was then raised to 280° C. over 30 min,followed by heating at 280° C. for 24 h. After that, the power of theinert oven was turned off while the oven door was closed and the airflow was maintained (20 L/min), the sample was naturally cooled for 12h, and taken out. As a result, a fluororesin heat-melted molded producthaving a thickness of 3 mm and a diameter of 26.4 mm was obtained on thePetri dish. At this time, air compressed by a compressor was passedthrough a dehumidifier (dew point temperature −20° C. or lower) was usedas the air. The transmittance was measured at each wavelength at 1 nmintervals at wavelengths of 200 nm to 1500 nm using a spectrophotometer(U-4100, manufactured by Hitachi High-Tech Science Co., Ltd.) for eachobtained fluororesin heat-melted molded product together with the Petridish. Data at 5 nm intervals at wavelengths of 380 nm to 780 nm wereextracted from the measured transmittance data, and the tristimulusvalues X, Y, and Z of the XYZ color system were calculated according tothe method of JIS Z8701, the yellow index (YI) under a C light source(auxiliary illuminant C) was calculated according to the method of JISK7373, and the yellow index (YI) of the fluororesin heat-melted moldedproduct including the Petri dish was obtained. The yellow index (YI) ofthe Petri dish (receiver only) alone was measured, and the yellow index(YI) of the Petri dish (receiver only) was subtracted from the yellowindex (YI) of the fluororesin molded product including the Petri dish toobtain the yellow index (YI) of the fluororesin heat-melted moldedproduct having a size of 3 mm. The yellow index (YI) of the Petri dishalone (receiver only) was 0.21.

Example 2-1

A solution obtained by dissolving 0.0432 g (0.000103 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator in 0.130 g ofhexafluorobenzene was placed in a glass ampule having a diameter of 30mm and equipped with a magnetic stirrer, 5.0 g (0.0205 mol) ofperfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 19.87 g ofZEORORA-H (manufactured by Nippon Zeon Co., Ltd,1,2,2,3,3,4,4-heptafluorocyclopentane) as a polymerization solvent, and0.556 g (0.00465 mol) of chloroform (manufactured by Wako Pure ChemicalIndustries, Ltd.) as a chain transfer agent were added, nitrogensubstitution and decompression were repeatedly performed and then theampule was sealed under reduced pressure (amount of chain transferagent: 10% by weight based on the total of the monomer and chaintransfer agent). Precipitation polymerization was carried out by holdingat 55° C. for 24 h while stirring with the magnetic stirrer in anupright state of the ampule, and a cloudy slurry was obtained in whichthe resin was precipitated in the polymerization solvent. After coolingto room temperature, the ampule was opened, the liquid including theproduced resin particles was filtered off, and the particles were washedwith acetone and vacuum dried to obtainperfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield:82%). The molecular weight distribution Mw/Mn was 2.5. Table 2-2 showsthe evaluation results of the fluororesin.

Example 2-2

A solution obtained by dissolving 0.0432 g (0.000103 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator in 0.130 g ofhexafluorobenzene was placed in a glass ampule having a diameter of 30mm and equipped with a magnetic stirrer, 5.0 g (0.0205 mol) ofperfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 19.87 g ofZEORORA-H (manufactured by Nippon Zeon Co., Ltd,1,2,2,3,3,4,4-heptafluorocyclopentane) as a polymerization solvent, and1.250 g (0.0105 mol) of chloroform (manufactured by Wako Pure ChemicalIndustries, Ltd.) as a chain transfer agent were added, nitrogensubstitution and decompression were repeatedly performed and then theampule was sealed under reduced pressure (amount of chain transferagent: 20% by weight based on the total of the monomer and chaintransfer agent). Precipitation polymerization was carried out by holdingat 55° C. for 24 h while stirring with the magnetic stirrer in anupright state of the ampule, and a cloudy slurry was obtained in whichthe resin was precipitated in the polymerization solvent. After coolingto room temperature, the ampule was opened, the liquid including theproduced resin particles was filtered off, and the particles were washedwith acetone and vacuum dried to obtainperfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield:80%). The molecular weight distribution Mw/Mn was 2.7. Table 2-2 showsthe evaluation results of the fluororesin.

Example 2-3

A solution obtained by dissolving 0.0432 g (0.000103 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator in 0.130 g ofhexafluorobenzene was placed in a glass ampule having a diameter of 30mm and equipped with a magnetic stirrer, 5.0 g (0.0205 mol) ofperfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 19.87 g ofZEORORA-H (manufactured by Nippon Zeon Co., Ltd,1,2,2,3,3,4,4-heptafluorocyclopentane) as a polymerization solvent, and0.435 g (0.0364 mol) of chloroform (manufactured by Wako Pure ChemicalIndustries, Ltd.) as a chain transfer agent were added, nitrogensubstitution and decompression were repeatedly performed and then theampule was sealed under reduced pressure (amount of chain transferagent: 8.0% by weight based on the total of the monomer and chaintransfer agent). Precipitation polymerization was carried out by holdingat 55° C. for 24 h while stirring with the magnetic stirrer in anupright state of the ampule, and a cloudy slurry was obtained in whichthe resin was precipitated in the polymerization solvent. After coolingto room temperature, the ampule was opened, the liquid including theproduced resin particles was filtered off, and the particles were washedwith acetone and vacuum dried to obtainperfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield:81%). The molecular weight distribution Mw/Mn was 2.4. Table 2-2 showsthe evaluation results of the fluororesin.

Example 2-4

A solution obtained by dissolving 0.0432 g (0.000103 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator in 0.130 g ofhexafluorobenzene was placed in a glass ampule having a diameter of 30mm and equipped with a magnetic stirrer, 5.0 g (0.0205 mol) ofperfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 19.87 g ofZEORORA-H (manufactured by Nippon Zeon Co., Ltd,1,2,2,3,3,4,4-heptafluorocyclopentane) as a polymerization solvent, and0.236 g (0.0197 mol) of chloroform (manufactured by Wako Pure ChemicalIndustries, Ltd.) as a chain transfer agent were added, nitrogensubstitution and decompression were repeatedly performed and then theampule was sealed under reduced pressure (amount of chain transferagent: 4.5% by weight based on the total of the monomer and chaintransfer agent). Precipitation polymerization was carried out by holdingat 55° C. for 24 h while stirring with the magnetic stirrer in anupright state of the ampule, and a cloudy slurry was obtained in whichthe resin was precipitated in the polymerization solvent. After coolingto room temperature, the ampule was opened, the liquid including theproduced resin particles was filtered off, and the particles were washedwith acetone and vacuum dried to obtainperfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield:83%). The molecular weight distribution Mw/Mn was 2.8. Table 2-2 showsthe evaluation results of the fluororesin.

Example 2-5

A solution obtained by dissolving 0.0432 g (0.000103 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator in 0.130 g ofhexafluorobenzene was placed in a glass ampule having a diameter of 30mm and equipped with a magnetic stirrer, 5.0 g (0.0205 mol) ofperfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 19.87 g ofZEORORA-H (manufactured by Nippon Zeon Co., Ltd,1,2,2,3,3,4,4-heptafluorocyclopentane) as a polymerization solvent, and0.155 g (0.00130 mol) of chloroform (manufactured by Wako Pure ChemicalIndustries, Ltd.) as a chain transfer agent were added, nitrogensubstitution and decompression were repeatedly performed and then theampule was sealed under reduced pressure (amount of chain transferagent: 3.0% by weight based on the total of the monomer and chaintransfer agent). Precipitation polymerization was carried out by holdingat 55° C. for 24 h while stirring with the magnetic stirrer in anupright state of the ampule, and a cloudy slurry was obtained in whichthe resin was precipitated in the polymerization solvent. After coolingto room temperature, the ampule was opened, the liquid including theproduced resin particles was filtered off, and the particles were washedwith acetone and vacuum dried to obtainperfluoro(4-methyl-2-methylene-1,3-dioxolane) resin particles (yield:74%). The molecular weight distribution Mw/Mn was 2.5. Table 2-2 showsthe evaluation results of the fluororesin.

Comparative Example 2-1

This comparative example was implemented in accordance with thepolymerization conditions described in Samples 92 and 93 in Table 2 ofNPL 1. However, the amount of the polymerization initiator charged wasset between those of Samples 92 and 93. A total of 0.017 g (0.0000407mol) of bis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 5.0g (0.0205 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as amonomer, and 8.2 g of hexafluorobenzene as a polymerization solvent wereplaced in a glass ampoule having a capacity of 75 mL and were sealedunder reduced pressure after repeating nitrogen substitution anddepressurization. When this ampoule was placed in a thermostat at 60° C.and held for 24 h to carry out radical solution polymerization, aviscous liquid in which the resin was dissolved was obtained. Aftercooling to room temperature, the ampoule was opened, and the resinsolution was diluted with 36 g of hexafluorobenzene for viscosityadjustment to prepare a resin diluted solution. A total of 1 L ofchloroform was added to a beaker equipped with an anchor blade, theresin was precipitated by adding the resin diluted solution to thechloroform under stirring, and the precipitate was vacuum-dried toobtain perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 66%).The molded product after heating at 280° C. for 24 h had a large numberof bubbles, but the coloring was stronger than that of Example 2-5 byvisual observation and weaker than that of Comparative Example 2-2. Themolecular weight distribution Mw/Mn was 1.9. The evaluation results ofthe fluororesin are shown in Table 2-2.

Comparative Example 2-2

This comparative example was implemented in accordance with thepolymerization conditions described in Sample 84 in Table 3 of NPL 1.However, NPL 1 does not describe the polymerization time, and in thisexample, it was set to 24 h. A total of 0.0578 g (0.000137 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 10.0 g(0.0410 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as amonomer, 16.32 g of hexafluorobenzene as a polymerization solvent, and0.0341 g (0.000286 mol) of carbon tetrabromide (CBr₄) as a chaintransfer agent were placed in a glass ampoule having a capacity of 75 mLand were sealed under reduced pressure after repeating nitrogensubstitution and depressurization (the amount of chain transfer agent:0.34% by weight based on the total of the monomer and chain transferagent). When this ampoule was placed in a thermostat at 60° C. and heldfor 24 h to carry out radical solution polymerization, a viscous liquidin which the resin was dissolved was obtained. After cooling to roomtemperature, the ampoule was opened, and the resin solution was dilutedwith 64 g of hexafluorobenzene for viscosity adjustment to prepare aresin diluted solution. A total of 1 L of chloroform was added to abeaker equipped with an anchor blade, the resin was precipitated byadding the resin diluted solution to the chloroform under stirring, andthe precipitate was vacuum-dried to obtainperfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 54%). Themolecular weight distribution Mw/Mn was 3.7. The evaluation results ofthe fluororesin are shown in Table 2-2.

Comparative Example 2-3

This comparative example was implemented in accordance with thepolymerization conditions described in Sample 78 in Table 3 of NPL 1.However, NPL 1 does not describe the polymerization time, and in thisexample, it was set to 24 h. A total of 0.0539 g (0.000128 mol) ofbis(2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator, 10.0 g(0.0410 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as amonomer, 16.32 g of hexafluorobenzene as a polymerization solvent, and0.1143 g (0.000957 mol) of carbon tetrabromide (CBr₄) as a chaintransfer agent were placed in a glass ampoule having a capacity of 75 mLand were sealed under reduced pressure after repeating nitrogensubstitution and depressurization (the amount of chain transfer agent:1.13% by weight based on the total of the monomer and chain transferagent). When this ampoule was placed in a thermostat at 60° C. and heldfor 24 h to carry out radical solution polymerization, a viscous liquidin which the resin was dissolved was obtained. After cooling to roomtemperature, the ampoule was opened, and the resin solution was dilutedwith 36 g of hexafluorobenzene for viscosity adjustment to prepare aresin diluted solution. A total of 1 L of chloroform was added to abeaker equipped with an anchor blade, the resin was precipitated byadding the resin diluted solution to the chloroform under stirring, andthe precipitate was vacuum-dried to obtainperfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 40%). Themolecular weight distribution Mw/Mn was 2.5. The evaluation results ofthe fluororesin are shown in Table 2-2.

TABLE 4 Table 2-2 Example Example Example Example Example 2-1 2-2 2-32-4 2-5 Weight average 8.7 5.9 12  19  27  molecular weight Mw × 10⁴Glass transition 131.1  130.1  131.3 130.5 130.8 temperature (° C.) Meltviscosity (Pa · s) 5.3 × 10³ 1.2 × 10³ 1.1 × 10⁴ 3.7 × 10⁴ 1.2 × 10⁶Defoaming property A A A B C Cracks after heating A B A A A for 24 h at280° C. and cooling Difference in weight  0.05  0.09   0.07   0.08  0.09 loss amount between after heating for 30 min at 300° C. andimmediately after heating to 300° C. Yellow index (YI) 1.7 2.0  1.9  2.5 5.6 after heating for 24 h at 280° C. Comparative ComparativeComparative Example 2-1 Example 2-2 Example 2-3 Weight average molecular73  6.3 1.0 weight Mw × 10⁴ Glass transition temperature 130.9 128.3 117.6  (° C.) Melt viscosity (Pa · s) 1 × 10⁷ — — Defoaming property F AA Cracks after heating for 24 h A C D at 280° C. and cooling Differencein weight loss   0.10 1.1 3.6 amount between after heating for 30 min at300° C. and immediately after heating to 300° C. Yellow index (Yl) afterLarge number 11.2  12.8  heating for 24 h at 280° C. of bubbles

The method for producing a fluororesin according to the second aspect ofthe present invention has a higher yield than the method described inNPL 1, makes it possible to produce a fluororesin at a yield of 70% ormore as shown in Examples 2-1 to 2-5, and depending on the conditions,and makes it possible to produce a fluororesin at a yield of 75% ormore.

INDUSTRIAL APPLICABILITY

The first aspect of the present invention provides fluororesin particleshaving excellent flowability and filling property and a small amount ofweight loss in heating and a method for producing the fluororesinparticles. The second aspect of the present invention is useful in afield related to fluororesins.

The invention claimed is:
 1. A method for producing resin particles, themethod comprising: obtaining a resin comprising a residue unit offormula (4) by placing a mixture of a radical polymerization initiator,a monomer of formula (3) and an organic solvent under a polymerizationcondition, wherein the organic solvent is a solvent in which at leastthe monomer is dissolved, at least a part of the resin produced bypolymerization is not dissolved, and precipitation of the resin occurs,and the organic solvent comprises a fluorine atom and a hydrogen atom ina molecule; and the resin produced by the polymerization precipitates asparticles in the organic solvent,

wherein Rf₅, Rf₆, Rf₇, and Rf₈ are each independently selected from thegroup consisting of a fluorine atom, a linear perfluoroalkyl grouphaving 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to7 carbon atoms, and a cyclic perfluoroalkyl group having 3 to 7 carbonatoms, the linear or branched perfluoroalkyl group may have an etherealoxygen atom, Rf₅, Rf₆, Rf₇, and Rf₈ may be linked to one another to forma ring having 4-8 carbon atoms, and the ring optionally includes anethereal oxygen atom.
 2. The production method according to claim 1,wherein the organic solvent dissolves the monomer of the formula (3) anddoes not dissolve the resin including the residue unit of the formula(4).
 3. The production method according to claim 2, wherein the organicsolvent is an organic solvent in which after resin particles comprisingthe residue unit of the formula (4) and having a weight averagemolecular weight Mw of 5×10⁴ to 70×10⁴ have been immersed at 50° C. forat least 5 h in the organic solvent an amount 10 times in w/w of anamount of the organic particles, a residue of the resin particles isvisually confirmed in the organic solvent.
 4. The production methodaccording to claim 2, wherein the organic solvent is an organic solventin which resin particles comprising the residue unit of the formula (4)and having a weight average molecular weight Mw of 5<10⁴ to 70×10⁴ areimmersed at 50° C. for at least 5 h in the organic solvent in an amount10 times in w/w of an amount of the organic particles, the solvent isthereafter cooled to 25° C., a resin sample remaining in a solid stateis recovered, and a weight loss ratio of the resin sample is less than20% by weight.
 5. The production method according to claim 1, whereinthe organic solvent comprises a hydrogen atom at 1% or more by weight inthe molecule.
 6. The manufacturing method according to claim 1, whereinthe monomer of the formula (3) isperfluoro(4-methyl-2-methylene-1,3-dioxolane) of formula (5), and theresidue unit of the formula (4) is aperfluoro(4-methyl-2-methylene-1,3-dioxolane) residue unit of formula(6),